It would be brilliant if you were to include the tree's functionality to the City generator as well as the improved building, land elevation and props assets. It would improve the quality of the maps immensly and honestly remove much need for eternal editing.

I think that adding too much detail to city maps will make them less versatile. Trees probably will be added in some form and amount, but it seems to me that people have very different ideas about where and how many of them there should be. One of my options is to make a separate "city viewer" (similar to the existing City Viewer but in 2D) to produce more stylized images from maps generated in MFCG.

That's fair enough. Though i would still say that at the very least, including some more detailed buildings (such as the roof style) in addition tot he trees wouldn't be too much. Most released city maps have some kind of detail on the roofs to stop it looking too flat.