More detailed zoning. e.g lower, middle and upper class zones for office, shops, supermarkets.

Regional Finance. The regions start with around $1 000 000 and you allocate funds to cities that you start. e.g start a new city in small area and allocate $50 000.
There should be two kinds of tax, city and regional. You have the normal 8% or whatever for city and then from the region view you could adjust the regional taxes, allowing you to allocate more funds to the different cities.
Stuff that is the responsibilty of federal or state should be paid from the regional funds.