A lot of people have been saying how the settlements and cities all end up looking the same, and boring cities in a game like this is not a good thing! I think one way to get past this would be to implement the ability to have more than one building design per building type.
For instance, let's say a modder creates three new designs for the building type "Hut/House/Villa". That modder should also be able to add a function to his or her maps that allow whoever plays those maps or adds that mod to cycle through each one of those designs when placing either a hut, house or villa. Even a random selection of different designs for building types would be okay. Just something to mix up the visuals of a city.
Going into the extreme, there could even be different styles for different functions that a city specializes in. Bear with me, this is an "in the clouds" suggestion to go along with my more reasonable initial suggestion. In my mind, a city that pumps out Arcane is going to have a more "alchemical" quality where as a settlement pumping out materials would have a more "blue collar" feel to it, and a city specializing in tech or economy would have different styles as well. This would help distinguish cities in different ways, while giving players an instant recognition of what each city is specializing in or producing at just a glance. I know that the numbers do that as well, but let's be honest, numbers don't make for an engaging visual.
This second suggestion isn't necessarily a usable one, but the idea that players should be able to distinguish what each city is specializing in at a glance is, I think, valid. It would add functionality and personality to a game that could use a little of both.