I think this should be more different amongst different magical schools. It seems to me that it is a poor solution for divine magic to be contingent on power internal to the caster given what it is supposed to represent. Arcane magic makes a tad more sense (especially for sorcerors) to be based on power internal to the caster.
I think the Runequest magic point system is a good deal more elegant than the D&D system. In RQ, magic is stored in magic points which equal the character's Power attribute (the RQ equivalent of Wisdom); the character regenerates all his magic points every 24 hours but does so gradually. So a character with a POW of 12 regains a Magic Point every two hours.
In a campaign I currently run, the priest characters have to hit very high Prayer DCs to get God to produce magical effects for them but the only limit is that one cannot pray for the same thing twice in the same day.
I think the Runequest magic point system is a good deal more elegant than the D&D system. In RQ, magic is stored in magic points which equal the character's Power attribute (the RQ equivalent of Wisdom); the character regenerates all his magic points every 24 hours but does so gradually. So a character with a POW of 12 regains a Magic Point every two hours.
In a campaign I currently run, the priest characters have to hit very high Prayer DCs to get God to produce magical effects for them but the only limit is that one cannot pray for the same thing twice in the same day.