I enjoyed the local gods discussion. I would be inclined to allow a follower of a local god to gain powers in other places by speaking to similar gods in other locations. For example, a follower of Amnur could make offerings and entreaties to water gods in other rivers, streams, and lakes asking for their aid. Depending on the nature of the local god, they might be required to make specific types of offerings, and might need to seek out lore or other priests to learn the desires and wishes of those local gods. There might be some other river gods which are already allies of Amnur, and more prone to aid Amnur's servants, while there might be others who have rivalries (e.g. two rivers which feed into the same lake or sound might be rivals for the affections of a lake or coastal god) and who are much less likely to give each other a hand. In an area that is particularly dark or corrupted, the local river god might be angry and malevolent, or sorrowful, or unpredictably moody, creating extra trouble. (That first level spell for sensing a river's mood could be useful in such cases, I would probably allow that to work everywhere.) So, rather than making such followers unplayable for PCs, it might create a lot of interesting subplots and intrigues, and make the landscape feel a little bit more alive. If you extend the reach of each god sufficiently (e.g. a river god's domain extends to the boundaries of the river's watershed), they might never be completely out of magic.