I am against reagents/material components for spells because it's basically mana in a more annoying, inconvenient form that confuses people and clutters up the inventory. At that point it's easier to just bring Mana back, and add a 10-turn cooldown to drinking mana potions.
I do like the idea of spells that take one or more turns to prepare before they're actually cast, and I suspect that Larian is also considering that.
I think that longer cooldowns for more powerful spells is another good answer. Forktong's objection to that idea is that people could just sit around and wait for them to recharge. I think that if they do so, that's their prerogative, but some people might not want to wait around for 5 real-time minutes (or more) doing nothing.
