stealth_nsk
Deity
It would be so much more difficult to keep track of the happy-status since the cities again would need to be treated individually.
You'll not need to track individual city happy status. It's just a matter of decision which building to use for happiness. If you have, for example, circus increasing happiness by 3, it doesn't matter where to build it. If you have building which halves unhappiness for the city, it's the same, but bonus depends on the city where it's built.
I think it would add more deep to decisions. I.e. you have 10-level production city (which grows slowly, but builds fast) and 20-level commerce city. For simple happiness buildings there's no choice - you build them in production city. But for unhappiness reduce you'll need to choose between faster build and larger effect.