[Kemal]

Don't forget that if you possess the holy city and have the shrine for that religion built, every city with that religion in the entire world will get you +1 gold to your income via the shrine. Also, the AI will sooner convert to the religion you have been spreading in its cities because it has more cities with that religion that way, giving you the friendship bonus and thus better trading options.

True, except that if an AI has a shrine, it will get money from your cities as well with that religion. On the other hand, in free religion, with a lot of religions present in a city, the happiness bonus can get quite big. Plus, there are the religious buildings, as you pointed out.

You don't pay maintenance for buildings, only for cities and units.

Having a civ take on other civics can be quite potent, it could for example destroy a large relationship bonus it has with another 3rd party civ because of "you have chosen your civics wisely" bonus, thus weakening relations between those 2 civs. But also, some empires are profiting more from certain civics than others, having the AI change civics can seriously hamper or encourage their development (and even your own). A good example would be having a civ adopt mercantilism, which (iirc) prevents all foreign trade routes, meaning every other civ gets hit commercially because it loses trade routes with that civ.