Didn't think too much on it, but the City State Improvements, esp the Monastery in the Exploration age can be bought in towns.
Gold, Science, and Culture (If not Augustus) can't be bought in towns otherwise.
Most of them, excluding the Gold and the Stone Heads, don't have their base associated yield as an adjacency bonus, so you're keeping the 2/5 science from the step pyramid, monastery or megalith going forward, letting you have a leg up on the competition the next age.
Granted, this is all RNG dependent, since you can't count on rolling the right city state every game/age, plus protecting them from the AI or other players once they see the massive gains you're getting from them, in addition to paying gold for each improvement.
Don't forget the Warehouse bonus, since it's just slapping additional gains on top of the main reason why the town is there, mining, farming etc.
Gold, Science, and Culture (If not Augustus) can't be bought in towns otherwise.
Most of them, excluding the Gold and the Stone Heads, don't have their base associated yield as an adjacency bonus, so you're keeping the 2/5 science from the step pyramid, monastery or megalith going forward, letting you have a leg up on the competition the next age.
Granted, this is all RNG dependent, since you can't count on rolling the right city state every game/age, plus protecting them from the AI or other players once they see the massive gains you're getting from them, in addition to paying gold for each improvement.
Don't forget the Warehouse bonus, since it's just slapping additional gains on top of the main reason why the town is there, mining, farming etc.
