Well, I can see how you think this, but I do not get why...
Is building a paladin tributing resources to another player, who gives you units in return? no, of course not...
Rather, it isn't like there are other players, why think about it that way? ACtually, you are the one buying the god power, and you are the one using it. I don't see how you get that realisation when you control everything about the gp, not the "invisible gods". It is your gp, and your favor. Its just like buying a unit...
now that I think about it though, this is not true. We just found favor does not buy gp. They come by the ages... So there is no arguement at all if you think about it, as favor is just for mus I would think