Cooldowns can be made quite long. A round is 6 seconds. A spell with a cooldown of 600 rounds will take a real-time hour's worth of play to wear off. I can't see someone wanting to leave a dungeon after every encounter because they want to use Armageddon on every 10 HP goblin encounter.
It would be even worst. The system would be equally exploitable trough rest and the developers should make crazy considerations about timing while designing a dungeon or a quest. A per-day limit would be 10 time less problematic. There are better solutions, though.
And no, seriously, reagents suck HARD. It's an obnoxious system on so many levels, ESPECIALLY if they're a limited resource. That will just end up with a system where the high-level spells requiring reagents will NEVER be used, because the mentality is "what if I need this for later?" Simpler to not have super-powered spells in the first place. Or only have those spells as Scrolls, not as spellbooks that you can learn and cast at will. That would function as the same limited resource as reagents would, yes?
If reagents are not an unlimited resource, then they'll just become more complex mana potions.
They're an inventory problem because you're adding in ANOTHER ton of sh!t into a game that already has a ton of sh!t you can combine with a ton of sh!t. I don't want to have to consult a stupid table every time I find something called "pinch of moth fart" to figure out what good it is, or if I should just toss it. It's STUFF OVERLOAD. Even with the items already in the alpha that I pick up and wander around with, my inventory is full of just stuff that I pick up because of game OCD and have no idea what to do with. I do not want to have to deal with reagents on top of that, especially if I'm not even using a mage.
. This is part of the Ultima-vibe that Original Sin is trying so hard to recreate, and there are bunches of people out there that love it. These are games where you can take, use, combine a shitload of stuff, even if you don't really need to. Is it over-design? Probably, but it's part of the reason because Ultima VII is among the best CRPG ever made. Casting through reagents can work in OS exactly for this reason. You already have lots of reagents in the game; you just need to convert them in a magic resource, and make the high level spells dependent from the rarest ones.
As for the "save for later" complex, reagents aren't worse than any other limitation. Cooldown wouldn't change anything in this regard.
