So here's my thoughts in more detail, regarding City-State Types & their rewards/missions:
Cultural: If you meet this City-State first, they'll grant you +15 Culture-or +30 if you meet them with a Scout. They will almost always have dyes, silk or marble in their proximity. When you become friends with them, they'll boost culture from Monuments by +1 each, & +2 when you ally with them. They'll also grant culture to your trade routes when you ally with them. Their missions will usually involve the construction of high culture buildings & improvements, producing Great Artists & the provision of certain luxury resources.
Agricultural: If you meet this City-State first, they'll grant you +15 food (in your capital)-or +30 if you encounter them with a scout. They will almost always have spices, sugar or wine in their proximity. When you're friends with them, they'll grant you a food bonus of +1 to any city with a granary, +2 if you're allied. They'll also grant food to your trade routes. Their missions will usually involve you building food related buildings, Wonders & improvements or supplying them with any of the food related luxuries they don't already have.
Mercantile: If you meet this City-State first, they'll grant you +15 gold (or +30 if you meet them with a scout). They will almost always have Gold, Gems or Silver in their proximity. When you're friends with them, they'll grant bonus gold to your markets, & grant extra gold to your trade routes if you ally with them. Their missions will usually involve construction of Gold Boosting buildings & Improvements, as well as the creation of Great Merchants. They will also be the ones most likely to ask you to build roads to them.
I could go on, but I'm sure you can see from the examples I've provided how I'd like to see City-States altered. Not sure about what impacts patronage should have-but I do think there should be social policies that make it easier to maintain friendships with City-States, just not as easy as they've done it

.
Aussie.