I think you are such a slippery slope here that is unsupported by anything in RAW. There is nothing that says a spell casting roll is a stamina roll. Nor does anything say that Ritual spells are any ability roll. Any roll vs an ability is vs a easy factor (ArM pg 6) Spell casting, any spell casting, is trying to get a total. Since Cautious with (Ability) helps with the ability roll it could not add to a spell casting roll.
If you can get your SG to agree with you. More munchkin power to you.
That's just it, though. Realistically, nobody could (given the likely lifespan of our sagas). If we were playing 40-past or if we had CrMe/CrCo specialists, these spells would make a lot more sense.
The very existence of these spells leads some characters down the powergaming trail, though. Knowing you can 'dump' stats for extra points for the stats you really want and just 'wizard' the stats back later is very tempting, BUT it's a trap. Having -2/-3 in several stats can be very problematic, especially where other flaws start to interplay (like Blatant Gift and -3 Com), and you basically have to build your character to use these spells to get them working in a reasonable amount of time. In the end you have a very 'powerful' magi, attribute wise, but the older magi get the less attributes matter.
Caveat: If your character concept demands several negative stats, by all means go for it. My point is that the "Dump now buff later" isn't as 'easy' as people seem to think it is, and distracts you from doing things that will actually make you powerful (Arts, Formulaic Spells, Enchanted Devices - these are the things that make powerful magi).
That's a valid strategy, if you can stomach being pathetically (physically) weak for a large portion of the saga. Personally, I hate having low stats in anything (never dropped anything below -1). Improved Characteristics is the easy way to be good in a couple stats without sucking in others - and you avoid the whole hassle of chasing down the stat boosting spells.
No, it's a really good virtue. Magic Theory is a huge limiter on magical activities (seasonal vis use), so Affinity/Puissant is a big boost for any magi - it's almost required for Verditus magi (it's a toss up between Puissant Magic Theory and Puissant Philosophae for Verditus, though Puissant Craft is almost as valuable).
SFB is really good, but putting those years at the front end gets you less than putting them at the 'back', so to speak. 225xp is really tempting, but keep in mind if those are pre-gauntlet years you can't spend them on Arcane/Academic/Martial Abilities (without another virtue that allows them), or Arts. You end up much better rounded as a person, but not much more powerful as a magus. Also, given how one bad aging roll can rack up Decrepitude, having 25 years or so post gauntlet without having to make aging rolls at all is pretty sweet. It really depends how your saga is set up. If you're starting fresh from gauntlet, the SFB magus can game the system to his advantage. If the GM says "You're all 50 years of age.", you're better off apprenticing as young as possible.
The instant death at 100 years, or whatever it is like that, makes it not as good for a magus in my opinion. Quite good for a non-magus, though.
I'm not so sure about that. Let's say I set Str -3, Dex -3, Qui -3 and let's say others do similar, how easy is it to earn back those points? It's a level-35 ritual to get one of those to 0. I've found usually someone is good at CrCo for healing, having specialized in either Cr or Co, even if not both. Now, you don't want to interrupt your life, but you do this just a few years down the road. Let's say one is 15 and the other is 8. Int +3, MT 6, Aura +4 (probably typical), Lab +6 (whether for spells, Cr, or Co). That's 42 already. Just a little more an it can be done in two seasons without ever having made much effort toward it. In my cases, I usually would get much more than Lab +6 because I love having labs specialized in spells. I get +5 from one Major Focus/Feature alone. You might also have an apprentice or a familiar for some bonuses.
You make sure you invent a Circle version. It costs 6 vis to raise a whole bunch of people from -3 to -2. Repeat two more times. 18 Vis to raise all your weak covenfolks' strengths from -3 to 0. Let's say there are six magi taking part, including yourself. You charge each of the others 6 Vis ahead of time (before embarking on the project, basically hiring you to invent the spell). So you collect 12 Vis and +3 Strength for two seasons of work, and everyone gets to raise Strength at 2 Vis per point.
How much of a distraction is two seasons of work for 12 Vis and +3 Strength? If you've ever distilled Vis from an Aura, you've probably distracted yourself more than this by doing so.
Oh, I agree. I was just doing that to show the relative value as a Virtue. I would never use up all 15 years like that for a magus because you can get even more for it.
Firstly, I think this situation is unlikely in the extreme, short of making it the focus of your campaign ("Weaklings band together to fix it"). And why would the other players 'hire' the Cr/Co specialist to create a spell that he himself needs so badly? I can see them sharing the cost of casting it if it's a Circle target, they might even cover the costs of casting it (so you get the benefits free, for inventing and casting the spell) entirely. But you wouldn't be up by 12 pawns at the end of it all. That's the kind of profits the guys with the +5 version can pull in, not the +0 version. You might get token payments casting the +0 version, but every pawn they pay you slows the whole process down (see below).
Second, a level 35 ritual is 7 pawns, not six, and so that's 21 pawns per stat, making it 63 pawns in total, and a minimum of 6 seasons inventing spells, and probably another 3 seasons mastering them (casting un-mastered rituals is a lot more dangerous), plus another several seasons buffing your lab and/or arts to get the 45 - probably a total of 2-3 years of prep work, assuming you already have a Cr and/or Co specialist. Also assuming you have no other distractions or problems (which, this being a RPG, happen).
Also, you need 63 pawns of Cr/Co vis (more if they are paying you fees - though the fees can be any vis), which by and large you cannot manufacture, and even if someone has Personal Vis Source most GMs peg them at 3-4 pawns a year so there's a 15-20 year threshold (unless all magi have sources, then it could happen in 5-6 years depending on how many magi you have). Magi could spend seasons creating Vim vis and trading it to redcaps at 2:1 for Corpus - but that's still more seasons put towards this effort. If you are lucky your covenant has a source of one or the other, but these are premium vis sources and go to things like longevity potions, creation rituals and wound healing. Since your Creo specialist is making spells, if you have a vim specialist maybe he can generate 5 pawns of Vim a season, everyone else is probably 4, if not 3. Call it 4 average, or 2 pawns Corpus once traded. So it take 31 seasons of extraction to get that much vis using extraction. Even if only 1/2 is extracted and traded, that's still 15 seasons (almost 4 years) of magi time.
So, best case scenario, the specialist has spent 2-3 years of prep time, the other people have spent just as much raising the necessary vis (if not more time), and none of you have accomplished anything else. You've used up 63 pawns of vis (which is about 7 longevity potions worth with a CrCo lab total of 45, or 5 talismans opened at MT6, or 6-7 familiars bonded or around 15-20 lesser enchantments).
And that's assuming you get to work uninterrupted, crisis free. Assuming your low Dexterity, Quickness and Strength doesn't bite you in the meantime.
So yeah, a LOT has to line up perfectly for this to be as 'easy' as people think it is. Years of time and many rooks of vis. And that's going the group way - going it solo is even worse.
Yes, 7 pawns, not 6. I had the level at 30 and forgot to fix the vis when fixing the level.
Yes, certainly quite unlikely in specifics. Also, note that most those seasons of prep work on the lab are were not for this but for whatever your main pursuit is, so those seasons are not at all wasted on this. Having been through something quite similar, I can say based on empirical evidence that the basic idea is quite valid. The issue is that it's not something everyone would do. Rather, a single magus could do it without taking an exorbitant amount of time and could rake in huge profits without charging a fortune. If a single magus could gain so much value out of the few seasons put into it (especially with Mercurian Magic, Flawless Magic, and/or Imbued with the Spirit of (Form)), wouldn't one? As soon as one or two would on their own and would want to sell their services since that's how they would profit, it's readily available.
Certainly not wasted, absolutely not, but still taken. I have varying opinions on the worth of laboratory buffing, though having a cool lab can be an end unto itself.
It certainly can be done, it's just not a trivial matter for the younger magi (read: most PCs). Any more than any hermetic project that would consume 50+ pawns of vis would be trivial, these are projects greater than your familiar or your talisman.
I would. I'm confident that some others would not. 
I've praised these three virtues lavishly in other threads. I neglected the MT enhancers in this thread to focus on optimizing specialists rather than generalists (and to follow the conversation about MM) since I think that's a better path for players new to the game.
Pu/Aff with MT also lets you use more vis, which mere Int does not. There are also a few mysteries that are capped by MT rather than Int. So totally agreed.
SFB offers everything you have mentioned, and also a heightened cap for Faerie Correspondence, which can be immensely useful. I don't know if I would appraise the package at +6 for magi, but it is easily worth its +3 weight. It even offers awesome roleplaying potential, hooking a character into Real Medieval Folklore. SFB can easily serve as the organizing idea behind a character, which is a gross understatement because it can serve as many different ideas, at least as many as there are kinds of faerie. (And why limit oneself to those listed in RoP:F? You can have Church Faerie blood, or Faerie Knight blood, or be the son of someone who lingered too long in Arcadia....) Every PC can take SFB yet have niche protection.
If a player is not sure what kind of character to play in Mythic Europe, I so recommend taking SFB and choosing a Faerie or fairy tale. Great for rp, great for optimizing, just great.
Anyway,
Ken
Hmm. I find myself disagreeing. I think the main value lies in putting those 225xp to use at the beginning. A magus is likely to live a very long time anyway, and is more likely to expire from mishap or Twilight. So taking those years later is not likely to provide any advantage.
Meanwhile, although all those xps are limited, many are useful. Concentration is simply good. Boosting Second Sight is also reasonable. Various other abilities do not directly boost a magus' power, but having a few clutch normal abilities at useful levels remains useful. Oh, and if the character has a correspondence, xps can go here too. BTW, you can use maxed out social abilities against other magi in Tribunal; trying the same with Arts is not likely to prove fortunate....
Minor point - Creo effects can't be circle - this would have to be Group. (AM5th, 113, "Targets and Creo" callout)
No, this is not true. Creo to create things de novo cannot be T: Circle. Reread that section you cited. Other Creo effects can be, and I believe there are canon examples.
OK. "A spell to create a part of something is either a healing spell or a Muto spell, depending on the part created." Point taken. It's not muto (by definition it's CrCo or CrMe) - so it's a healing spell (sort of - in the "make it better within it's Nature" definition of healing) targeting a specific aspect of the individual. It therefore needs to be Part (+1), as opposed to Group. Except that according to the description of Part, "A person's mind is not a part of him in this sense, nor is his sense of humor."
So it seems to be somewhat unclear. Can you indicate the canon examples?
Creo can create things or it can make something a better version of itself. Spells that create things must use T:Individual or T:Group.
Should have been written like this, as the two sentences are not directly imo:
Creo guidelines
Because spells that heal are not subject to the second dot point from have I have observed.
I think the mistake is to assume that the sidebar on page 113 applies to all Creo spells. I don't believe those rules are written to, rather they apply to any Creo spell that match certain criteria.
The target limit from page 113 only says it applies to spells that create actual things. The characteristic spells improve things that already exist, so I don't see why that rule should apply. They are also not written as Target:Part spells so there is no reason to try to classify them as such. Beyond that their is nothing in the pg113 sidebar relevant to the improve characteristic guidelines. Don't worry about it black swans exist.
That being said it's still pretty cheesy to try to mass produce the effect. But this is not the first or last cheesy effect that is well within RAW. You can always Rule One it away if you don't like it. It's also somewhat self limiting given the warping potential.
Warping potential? 8 points to go from -3 to +5. It's not a huge amount of warping.
I do agree that such a reading does seem to make slightly more sense. However - are there any actual canon examples of this?
Huh. In reading through the Warping rules - you pick up a warping point if the spell wasn't designed for you. Could you use a MuVi spell to say "This spell is now designed for the target?" I would imagine it would have to be a unique spell for that person. Ie, if you had 4 magi in your covenant, you'd have to have 4 separate MuVi spells. However, if this was the case, I'd argue that it would be considered a "minor" change, and thus available at 1/2 magnitude of the target spell: It's almost literally the exact same spell, only optimized for one person. (Of course, if the target is a ritual, the MuVi effect would also be a ritual. So there's the additional Vis cost. Another reason for Mercurean magic!)
Kevin where is that ruling? I've missed that if its in core, and it sounds darn handy.