I revisited a couple of the old city-builders: Caesar III and Zeus.
One of the things about these games is how everything functions as closed loops. People harvest food and eat food. They shear sheep and purchase wool. They demand culture and attend the theater.
Where's the waste? Where's the inefficiency?
There is an assumption in these games that expansion is linear. A cluster of houses will be supported by a fountain. Another cluster will need its own fountain. But the number of fountains won't put a strain on the whole system. And everyone seems to use everything properly. Fountains aren't busted by morons or vandals.
I don't know if the most recent SimCity took fluctuating stresses and exponential system growth into account. That's something I'd like to see, though.
I want to see the vast differences between social/economic classes, not just housing upgrades. Holidays should increase demand across the board and produce a lot more waste. Upper classes can support leisure pursuits but put more strain on basic services - more consumption, more waste, large social events, big families, servants.
Maybe that's too much for a game. Dealing with a chaotic system would probably be heavy on challenge and light on game.
I can barely sustain a city in Caesar III as it is.