Hey, everyone, thanks for all the replies. Most of this is untested, yes, and some of it's definitely overboard. I actually thought about it quite a bit in bed last night.
The genesis of 3d6 for spells for Guise of the Dragon was basically, originally they were going to lose spellcasting ability. Then, I thought, "but aren't dragons actually known as powerful spellcasters?" and threw that in. But I'm doubting it actually needs casting at all, now, and "While you maintain this form, you cannot cast spells." might be just fine.
For dice-modification precedent, I looked again and I think the closest is the add-a-die and take the highest, and I think that's only for weapons.
Regarding Perfect Recall, yeah, it's definitely too good. One thing I was toying with was "While this spell is active, when you roll to cast a spell. on a 10+ the spell is cast without trouble. On anything less than 10, you burn the spell from your mind; you can never learn, prepare, or cast that spell again. Furthermore, on a miss, this spell ends.". That makes it interesting (to me!) and provides a serious risk and element of choice to the wizard in question.
Arcane Storm, for Evokers, is another problem spell, but I'm not sure what to do with it. It's clunky and too-good.
- Alex