As long as Arts are based on XPs, we will see older magi gain very high scores in Arts, as well as highly specialised younger magi.
We can debate the advantages and disadvantages all year long - and more I'm sure - but Arts are higher now than they ever were n the 3rd edition, simply because no season is truely wasted and because there will always be books to learn from.
Oh so agree...
I like to cap items penetration to the lower of x times casting total in the relevant arts (+ focus) and PenetrationY. This makes them still powerful, but sets a limit.
This can be the lower of 1Casting Total or Penetration*10
Or it can be the lower of 1/2 Casting Total or Penetration *05
You get the idea
And to think that over there, I've got someone arguing with me that there's no problem with the RAW, might and might-strippers 
Looking through older sagas and scenarios I found a few other ideas I have been juggling with, but never had the need to use in a Saga:
Of these I think I like the "stronger at home" idea best. It lends itself to many stories where you need to get something or someone really powerful to go get the critter and sneaky stories to get an arcane connection and to stories about luring it out to get it when and where it is at its weakest.
There are different ways to increase MR of creatures without increasing their Might score. Doubling, tripling and more is only one option.
Other alternatives (on the fly, not polished)
Spending a might point acts like a WoM. So a might 20 creature can resist 20 spells if he does not use any powers of his own. Generally enough to resist you during a confrontation encounter.
MR does not exist for critters. Instead their Might is add3ed to their soak against magic effects (direct damage) or the magnitude of their Might is added to their resistance roll if it is indirect effects like ReMe. So a Might 10 creature adds +10 to its soak vs a POF and gets an extra +2 to resist your controlling spells either mental or physical. Combine with the above WoM power for some fairly high challenges.
In fact, parma could act like this (in-built WoM and adding to soak)
Partial Might strippers do not exist. You either destroy the creature outright or your spell has no effect. It is an all or nothing spell. So a Might 5 DEO is quite worthless. it does not solve the outrageous penetration totals of magi at medium/high levels, but makes destroying a Might 30 creature somewhat more complicated.
Penetration multipliers are no longer multipliers. they only add +1 to +5 per AC/sympathetic connection etc etc. That decreases penetration a lot if it is a SUM of stuff instead of a sum and then a MULTIPLICATION of stuff.
There 
Some random ideas.
Cheers,
Xavi
Overall, MR is either too low or needs some changes or most supernatural creatures gets easily curbstomped by anything beyond apprentices.
As i´ve mentioned before, with mightstrippers being the really bad ones, i´ve had them so that they only do damage based on how much the base level is above the creature might, and creatures takes damage on might pool first and can replenish that by reducing Might, but MR is still always counted on original Might.
And destroyed might doesn´t kill it, so it can still run off and heal up.
For other kinds of spells, i use at least Might/5 as bonus soak/resistance(or smaller divider if suitable for some reason, up to using Might as a whole as a bonus).
Not a perfect solution, but it can make a Might 20 Big Bad Magic Wolf that prowls in the forest a SERIOUS opponent.
Why not capped by the creator's Casting Total + Penetration - Spell Level? E.g. a magus makes a Wand of Demon's Eternal Oblivion at Level 10. His PeVi Casting Total is, say, 30, and he has Penetration of 4 (with a specialization "Demons"), while his PeVi Lab Total (with S&M and other bonuses) is 48. (Just making up numbers here, I know the math isn't perfect, but basically enough to put 8 points into Penetration). Would the item be able to have +16 Penetration, using the item creation rules? Or would the item only be allowed to have 4 (or 5) Penetration? Or would it be 10 (going off the creator's Casting Total)?
I like to have the extra stories of getting the arcane connection (and the sympathetic ones) to get high penetrations. So my gut-feeling is that if you're standing there face to face casting your spell, you get to use your raw power (penetration=casting roll + penetration - spell level). If you make a generic item, you only get your penetration score (yes, this limits the use of generic items against beings with resistance).
If you want the best of both worlds, you need to do the story to get the arcane connection, researching the sympathetic connections and making a dedicated item. But then you will get all the multipliers you can scrape together. The advantage to just making a spell at Arcane range is that you can spend much less on the effect and more on duration (to use an arrow should let you make the kill effect at touch instead)
I have much less trouble with an "arrow of Slaying Puff the Horrible Faerie Dragon living in the volcano next door" being able to kill Puff in one shot than having a full quiver of "Kill anything with faerie might I might encounter".
It is very much a YSMV thing, but my feeling for the myths is that the generic items should be utilitarian (?) and the very powerful ones should be very specific.
Hope that explained a little of why I do it that way. It's all about how I want it to feel.