Sure, in 3E that would be a good way to handle spell acquisition. In 4E, where most combat-related powers are integral in some way to the classes, there are "rituals" which handle traditionally non-combat applications (and which are more far-reaching in scope); rituals could be entirely the province of the spirits. You need a divination or somebody brought back from the land of the dead? You have to find a spirit of appropriate power to do the deed. And what it wants in return may be quite interesting!
In Old School D&D you could just divorce the conditions of spell acquisition from explicit mechanics: at 1st level a Cleric usually starts with no spells (or only 1, depending);... you could say that his "spell list" is empty or only has 1 entry related to his patron shrine (if you know "Cure Light Wounds" then it is a spirit that can heal, etc.). The Cleric can add to this when he goes on further adventures and negotiates with spirits.
Though I'm actually inclined to write this up for 4E Essentials... one interesting thing about 4E is that the monsters have diverse and flavorful powers (though there's no reason they cannot have those in other editions, obviously). But this setting would require monsters that felt quite unique.
This setting would also allow normally dumb monsters to be given personalities. Just because the spirit looks like an owlbear and has those stats doesn't mean that he cannot talk, or is stupid like a stock owlbear. Maybe he's a sage, maybe he's grumpy, maybe he's rapacious... maybe all the above.
In Old School D&D you could just divorce the conditions of spell acquisition from explicit mechanics: at 1st level a Cleric usually starts with no spells (or only 1, depending);... you could say that his "spell list" is empty or only has 1 entry related to his patron shrine (if you know "Cure Light Wounds" then it is a spirit that can heal, etc.). The Cleric can add to this when he goes on further adventures and negotiates with spirits.
Though I'm actually inclined to write this up for 4E Essentials... one interesting thing about 4E is that the monsters have diverse and flavorful powers (though there's no reason they cannot have those in other editions, obviously). But this setting would require monsters that felt quite unique.
This setting would also allow normally dumb monsters to be given personalities. Just because the spirit looks like an owlbear and has those stats doesn't mean that he cannot talk, or is stupid like a stock owlbear. Maybe he's a sage, maybe he's grumpy, maybe he's rapacious... maybe all the above.