i can kind of see an argument for it, because at the moment i'm struggling to work out what, if anything is determining population growth rates. i would like to feel i had some control over it.

however, i think the existing game mechanics need to be balanced and refined before any new ones are added.

I agree that population is an untapped pool of potential to make those large cities more special and make the level one city spam less worthwhile. Taxes would be good i think, there's a need for a population morale and rebelliousness mechanic, and probably more I haven't thought of. I think higher population is already boosting influence (or to be more precise leveling your city level is) but there is room I think to boost this further. The main reason I am spamming level one cities is to make sure I have good influnce coverage to get the monster spawn pushed back from my empire and I'd prefer to just have fewer, larger, more influential cities instead.

For better or worse, it seemed to be a conscious design decision to avoid sliders and infrastructure micromanagement in this game.  They wanted everything based on simple additive construction.

I'm personally not opposed to the idea in principle, but it would represent a fundamental change to the game philosophy.  With how much micromanagement we have in the late game just controlling units, I'm not sure more kingdom micro on top of that would be a good thing. I don't think you can just add this in, without shifting a bunch of other stuff too.

I agree we need taxes simpley  because I am unable to generate enough gold to build a feasible army.

I think perhaps cities should either have a base value dependant on size (+1 gold/wood/etc per size) or that buildings should have a base value as well as increased percentage value.

Also you could increase the overall influence and resource range of larger cities to emulate a more Civ-style sort of gameplay. IMHO advanced structures like barracks also need to increase recruitment speed drastically. As of now, yeah, it's definitely worth plopping down 10 cities to have ten units building.

IN the XML files you can see that before cities used to cost essence to build, I think that's a spectacular way to price them. Honestly I don't even think that's neccesary, a flat gold/materials fee would be fine. You might also want to increase pioneer build times and cost. Then there -would- be the same sort of 'time' penalty for building extra cities.