Now I've always taken the "luck as more a factor" bit to be gamespeak meaning, rolls you don't add abilities or characteristics to.
Now there are certainly a few situations that can crop up in the practice of hermetic magic that are governed almost solely by luck, (and rolls that are not generally modified by abilities and/or characteristics.)
Off the top of my head I can think of.
-Studying from Vis
-Effects of Twilight (The Good Stuff List)
By Raw it is entirely within the SG's purview to apply Luck when and how he likes.
My Own troupe has applied Luck to experimentation rolls in one way or another for awhile. When I SG I usually come up with some sort of elaborate bidding mini game system. The other guy who SGs our games just smiles when a player reminds him their character is lucky and uses it as an excuse to nudge the result into more interesting territory.
As far as any of the ones mentioned above goes what's the thought? Inappropriate interpretation of the situation?(maybe) To powerful for a minor virtue (probably). Finally a reason to take Luck. (When else does an SG call for an important roll that isn't tied to a stat. 1-5 the bandit shoots you, 6-10 it's shield grog Biggus Targetus)
I wouldn't normally apply it to Experimentation, Twilight, or Studying from Vis. I don't think it matters if you do, but to me they seem more things that are a matter of luck only from the player perspective; from the character perspective they seem to be matters of skill, intelligence and planning.
We normally apply Luck to rolls like "avoid being hit by a tree that suddenly falls across the path" (it's Lucky the character wasn't standing there), "staying awake all night when keeping vigil" (it's Lucky the character was actually awake when the important/interesting thing happens), "desparately trying to avoid falling off a cliff" (it's Lucky, the character gets snagged on a tree branch), etc. And whenever something bad happens to a random character, the chances of it being the Lucky character are lessened.
Also we tend to use it when the character attempts to use an Ability in somewhat dubious circumstances usually things like: Stealth (say, in broad daylight), Awareness (say, when actually looking for something else), Hunt (say, many days after the tracks would normally be obscured). Finally, we tend to use it to minimise the negative impact of Botches --- perhaps a Botch might result in a character dropping his sword in combat, a character with Luck we'd probably allow a Dex roll (or something) to narrowly avoid dropping it.
I probably wouldn't normally apply it to spell casting directly, but might apply it (in the right circumstances) to some of the rolls peripherial to spell casting (Aiming rolls, other Finesse rolls, Spell Concentration rolls, Fast Cast Speed rolls, etc).
See I've always played it that the Characters are perfectly aware that things like the results of experimentation are a crapshot. As are the benefits of a successful twilight comprehension or what happens when you try to study from vis.
It would be fairly obvious to a Magus that one's intelligence or skill at magic theory
has little bearing on what effect experimenting has on their project. A rank apprentice working on his own project for the first time is about as likely to get X result as an Archmagus. What really does matter is how much risk you take, And setting the level of risk is something any hermetic with a modicum of training knows how to do.
Sure like any gamble people will often attribute the results to various unrelated conditions. (Yes I roll d20's as d10's, I don't care what you say, I get better results with them.) But in the end a characters belief that intelligence and planning are why you got a particular modified effect would be as accurate and provable a players dice superstitions.
Not that it matters what the character thinks anyway. A Grog might think his success with dice is because of that little flick of the wrist he learned back in venice. He's wrong though he just has the luck virtue.
Depends on what you think is happening when a magus experiments in the lab. If it is truely just randomly mixing things up in the Lab, then sure it is subject to luck. However, I believe that in character, a magus who is "experimenting" (baring the odd crazy one) is thinking carefully about what they are doing and attempting to extrapolate beyond their current understanding.
You are right that the game mechanics for experimentation don't take into account the skill of the magus. However, under what circumstances a magus chooses to experiment usually relates to his skill. For example, an apprentice might need to experiment to be barely able to complete a magnitude two effect in a single season. On the hand, a master can probably do that without needing to experiment. When the apprentice experiments he is trying extrapolate beyond his current understanding; but the master doesn't need to because he already has a better understanding. Of course, the master might choose to experiment anyway (on a magnitude two effect). But that's because he is after some new way of doing something (perhaps fishing for a discovery, or some other result). He already has sufficient understanding to actually do the task. Characters with different skill levels tend to experiment on different things.
But having said all that. There's no drama if you do want to apply Luck to Lab Experimentation. I just wouldn't routinely do so.
So far no magus has had this virtue in my troupe. I do not see any problems allowing it to seasonal activities, twilight, experimentation or whatever like that. To me it sounds reasonable that it does apply. It is not like the ars laboratory system cannot be abused or anything like that, after all.
It wouldn´t apply on for example a roll on studying Vis no. But for experimentation, it should have a small chance to apply to some degree at least, Luck is a HUGE part of real world success in experimentation after all. And if the experimentation turns into a disaster or something, then Luck should definitely give a chance for making things end up better than without it.
That's part of why I think we started using Luck in experimentation. By RAW the Experimentation system really can't be exploited by a player and is holds little benefit for the character. The charts are mostly bad results. Most of the good results are moderated by the SG. The bonus you get to the lab total pretty good but the risks mean your almost never going to experiment on "vital" lab work.
As far as using Luck in Vis study. Well IMHO that system needs all the help it can get.
Ehh.... I don't know, my best Experimenting season I managed to get 30xp in Magic Theory, 15xp in Awareness, raised my Corpus from a 13 to a 14, and had my spell completely altered by the experiment and became the single most used spell in the entire saga. ((Touch range teleport a league spell... offense and defense hot stuff))
As a matter of fact I have only had one season where my experimenting went bad.... oh and it went really really, I mean really bad. hahhahah ((I blew up the lab and paralyzed myself for a entire season. Had to be spoon fed and this sounds not so bad except ALL of the covenant hated my magus. He took some lumps that season.))