So thus Divine casters have a completely static spell list which can never be altered except by the Gods?
I dunno if I really like THAT idea. So Bane comes up with a spell called Blade Barrier, and then his followers just somehow know to begin praying for it. The other Gods see Bane's followers casting Blade Barrier, and then they grant this spell to THEIR followers as well. Seems kinda silly.
This is all just my opinion... bouncing ideas off you guys. Suppose instead that the CLERICS come up with the spells, the gods just provide the energy and the means to cast them. For example, Jozan prays for "the power to smite his enemies with beams of light from his hands". The prayer invokes how the power from the god will be used. In essence, he's praying for "Searing Light". Now, if he wanted to pray for a version of "Searing Light" which was composed of negative energy as opposed to Light... well, Jozan hasn't been taught a prayer for that kind of power before. It's going to take some meditation and research into religious texts to determine exactly WHAT kind of power he should ask be granted to him. He doesn't want to request a power too high level for him, or too insignificant either... finally, after some research into it, he's sure of the exact type of power he must pray for. He does so, and has thus researched "Baneful Light" or whatever you want to call it... a 4th level spell that acts like "Searing Light" only it is composed of Negative Energy. Jozan can now teach the means to pray for this spell to other clerics. If his god is particularly pleased with Jozan and his new spell, he may inspire other clerics to pray for it, and then other gods may start granting it to THEIR followers, and so on.