Whereas I think that the having two different levels for temporary and permanent effects is self-contradictory under the Hermetic frame-work. It's clear that the levels are set as high as they are for game-balance reasons, rather than an in-setting justification. I also agree that they're too high, in as much as temporary things should be fairly accessable. I'd rather propose that you simply rule that Permanent ritual spells cause warping to the target proportional to the number of Pawns of vis used. It makes healing spells a bit more of a last ditch option, and favours spells which simply improve and speed healing, but it also means that any magus wanting to boost his stats pretty much guarantees himself twilight and a lot of warping which in turn shortens his life a great deal. That way I can see a mage being prepared to burn off a few years of life to get rid of a major penalty (which is a pleasant story event) and means that only the most insane or dedicated Bonisagus would actually try to boost himself all the way to Str or Int +5.
Instant healing being dangerous (but useful in extreme circumstances) is to me far more mythic and appropriate than a mage being unable to make himself temporarily stronger or faster.