@shoi: Thanks for sharing that mod, that's actually exactly what I was thinking

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@rulner and chrome:
I think that there should be different types of CSs, since there is one of warmongering empires, and one for cultural empires, there should also be one for science, productivity and commercial empires too.
Science CSs:
I agree that science per turn may be too strong, which is why I would prefer a bonus which is similar to the culture bonus... Like +6

in starting eras, maybe going up to 8-10

, but staying around that area.
Production CSs:
Production CS would be very nice in the beginning, giving a small but useful boost. Later in the game this could go up a little by era, but not by much! Maybe from 5

in early eras to 7-9

later. I feel that in reality, peace with city states is very important, even today, just look at our world today!

. And about them being too important later, well, this bonus would actually be much less significant later on, since you'd already have so much production, even with the era boost.
Commerce CSs
I agree with the part on commerce being an issue, but think of it this way... You are basically investing, say 500

, and getting a certain amount back over time. Or, if you were to use the CSDM mod,

will stop being such a contradictory thing. For those who don't know, the CSDM mod's idea is (and rightfully so) to stop putting gold gifts at the center of CS diplomacy, because that's just unrealistic! So there are other ways to make peace with them, and then

wouldn't seem like such an issue

. Or, this gold bonus could be based on how many cities you have connected to your trade network.
Alternative commerce idea:
ALSO, an alternative, make it so that CS's give you a bonus in commerce based on what monopoly buildings you have! Basically, if you're better at trade, you get better bonuses on this. I'm not decided yet whether that should be just commerce CS's or all of them, but I think that this should emphasize the importance of TRADE with CS's... And since the way diplo with CS's works now with gold is a big joke, this monopoly tradeoff would make even more sense with the CSDM mod!
The new bonuses in not just another CS mod:
I also really loved the addition of great-people CS's and diplomacy CS's, though IMO, this shouldn't be a dedicated CS, rather a small bonus that may or may not be added from certain CS's based on their personality, eg. a scientific CS that is also peaceful, and therefor give a diplo bonus

. Or a productive CS that is also progressive (gives you more gold-age points).
Importance of CSs:
I understand that some of you feel that CS shouldn't be so important, but I feel that CS have, and always will be, an important part of any empire. They do, after all, take up so much space on the map. And this would add such an interesting part to the game. I also feel this would give people much more respect to the CSs, and not some annoying obstacle that keep spamming units and blocking you

. Most importantly, we're looking to make the game more epic. What else would make the game feel more epic than more interactivity with city-states?
OH, and last idea, we could also have a mission of a city state be to be the first to make a breakthrough! Cool, huh?

.
What do you guys think of my ideas? I enjoy all your responses, it's nice to share my brainstorms!