So far i've been enjoying the air battles and ship building immensely, but i get the feeling that each city having it's own "trait" makes the game a little stale as you just take a city and get its tech advantage.
My suggestion would be making it so you could research basic technologies and you would need to capture certain neutral points of interest to get the more advanced stuff, essentially making certain points on the map much more attractive then others.
research could be done by spending some of your upkeep to a certain limit per city small to large. and maybe added city affinity to replace the current traits
Yes, i think the state if singlepalyer right now is kinda wierd too as you sometimes cant even unlock all the modules (could be meant to be) but a research upkeep could also resolve the flood of money when you have around half of the map
Agree with this as well, research would be kind of cool.
That could be a good way of doing it, yes. I kind of like the elegance of "1 city = 1 tech", but OTOH it also means that each city you face only has one special tech, which is kind of weird.