I hate subscriptions but you can offer something like that for x days for price Y, same thing but not named like that
, but you know one fun way to make all cities unique would be to change the roof colors on residences and worshops, another skin for your armory.
Easy modifications that would allow so much more individualism in each city, and that would target the casuals and the masses and it takes 0 extra time in art design for resisdences and workshops and a little for example the alternative skin for a armory but that pays itself back easy.
and you only need to build the system once.
Many simple easy cheap things to individualise your city.
Having options to customise your avatar with a hat, glasses, hat whatever, thats how microtransactions should work.