Having a few rare, forgotten spells only accessible via scrolls would be nice, though I'm not fond of requirements on scrolls. Because without these requirements, your proposition just entirely makes the mage class/tree useless, as one'd better put all his points in warrior stats since he gets all the mage stuff with scrolls.
Yeah, especially powerful scrolls could have Stat/Ability requirements on them, and while I'm not certain this is a good idea, maybe Scrolls AP cost should be equal to the spell's AP cost plus 1-3 additional action points. With that, the fact that they're one-time use and cost gold/luck to acquire should be enough to balance them.
Also a major difference with regeants is that spells use several different reagents, forcing the player to make a choice between which spells he'll use or which potion he'll craft.
That's one of the reasons why I find that system annoying, yes. EDIT: Specifically, needing to have certain amounts of 2-4 components to cast a spell. Typically that's the kind of thing found at random.
Except for the fact that in a per day system your are supposed to sleep to regain your spells. It's not just a mater of time. This way developers can control the ability spam through rest areas placement, and at the same time they are free of consideration about timing.
Which is something that you can do with the click of a button to your homestead? I don't see the meaningful difference. Neverwinter Nights 2 supposedly had a system like that, but in practice, you could just rest after every encounter.
Rare reagents just means difficult to find, not limited to a 2 digits number. We are talking of a renewable resource. Just rare, or expansive, or both, not a finite one.
And why more, excuse me? In Ultima, for instance, potions and spells use the same base ingredients. Leaving alone the fact that "you don't want to add more stuff in the game" isn't really an argument here, considering that putting an arbitrary limit to the amount of stuff one carries around in this kind of games is - in short - contrary to their spirit.
I'm not a fan of reagents because it adds annoying complication for no real benefit. Instead of having to worry about one item, your mana potion supply, you have to worry about your supply of 10-20 or more different components, each of which is used for multiple spells in different combinations and amounts.
A scroll-based rare-spell system would have you carrying around more than one thing, yes, but a scroll is only used for one spell, and using it won't affect your ability to use other spells.
