There's a game that I play from time to time called - All my gods - All My Gods > iPad, iPhone, Android, Mac & PC Game | Big Fish (bigfishgames.com)
I would really recommend you play it to see how they handled the situation - there are challenges, obstacles, you earn Mana, but it keeps you engaged. It has an interesting story line. It's a similar concept to what you're describing. It would in any event give you a lot of ideas for features to add to your game.
I like your idea of keeping people happy else they leave - that's not in this game - in this game the people have a protest which is by and large harmless. If they held a riot instead that could also be a fun feature - to have them go out and destroy or burn things down so it costs the player time and money to build up again and creates an incentive for them to keep the people happy.
Collecting resources is an option, or you could study something to advance technology. Alternatively if things break down, then the player has to keep a careful watch to fix them before they completely destroy i.e. if you don't fix the roof, then the building is destroyed. If you don't put out a small fire then the whole house burns down. It also uses up the resources so that the player needs more and doesn't in the end have a lot of money or "belief" and nothing to spend it on.
The game I mentioned also gives you options - like in your game, people trade with each other and that earns gold, they mine for gold, or you can use mana (i.e. belief) and it's up to the player whether they choose to fund something with mana or gold - whether they tell the people to put out the fires with water - or if the god uses mana to put out the fire. That choice will also keep the player engaged - because that gives them control - and then if they make the wrong choice they can run out of the one resource - so that also gives them an incentive to play again, to try and make better choices.