whats wrong with cooldowns that prevent using uber-spells more than once in a regular fight but let us use such spells in every fight? if there is a one-shot spell, nerf the spell but do not include a dump, silly and foolish resource system which nobody really needs.
Probably the fact that being able to cast your uber-spell on any 1 level goblin that crosses your way is dump, silly and foolish combat gameplay? Of course, maybe I'm wrong: this is just an hypothesis

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PS: by the way, I can't understand why people that can't stand to resource management bother to play an Ultima-like RPG in the first place? The mainstream market is full of Dragon Age-like crap that allows you to cast your uber-spells as much as you want. If I were you, I would look to Inquisition for having "fun" with magic.