I did not play vanilla that much, as I went right into this mod as I bought the game. But, I'll just tell you what I noticed. It seems that in the late eras, we get too much of everything, (if people reached 256k like stated, isn't it too much?), and it affects things such as city states. If you gain 5000 gold a turn and you only need 1000 gold to max a city state, that means you can ally with 5 city states a turn, it's a little too easy.
Would it be possible to change this cost depending on the era? Because right now with the fixed price, in ancient era you can't even bother paying a city state, and once you hit renaissance it becomes a joke. Or simply, make an average of every civ's gold per turn generation, and use this average to determine the cost for "buying" a city state. This way, only the civilizations considered wealthy IN THE CONTEXT would be able to spend money on such things. Because we all know, contexts differ a lot, if you put 3 civs in a huge map or 18 civs in a tiny map, the civ's money will be totally different and I think we need to account for that.