You can't just make stuff 'look nice' without affecting how the player behaves
I agree, and that's why a city shouldn't look perfectly spotless. A little weathering here, some extra foliage there, a bit of dirt on the street, etc... These details send exactly the right signal: A real city that feels lived in. Not artificial, not abandoned either, but a lively middleground.
> Will I be able to tell the difference between ‘weathered’ and ‘abandoned’?
Artistic nuance is required to find the right balance, of course. But, imo, abandoned buildings in Cities Skylines already stand out enough, not just because of the icon, but also because they're much darker in color. That leaves enough room to make regular buildings look a little more worn without blurring the distinction.
I had an argument at one point, honest!