While this may not be useful for direct encounters, I think the presence of these critters would provide excellent flavor for a region in some campaign world.
Of course, it could be that they provide necessary ingredients for some alchemical concoction that the PCs desperately need, or that one has swallowed an important item (possibly while ridding itself of an annoying scholar) which must be retrieved.
I have always liked the concept of the genius loci, especially as portrayed in Shintoism. Good sub.
It might be good to clarify the limitations on receiving help from the local spirits. Is it because, as Moon says, she is already claimed? Must someone be born in DC and be specially trained? Or, would it be limited to descendants of the original tribes of the area?