There seems to be no other thread for this task here, thought this seems an interesting idea.
So far, the best solution Is using blended cities like this. I am talking about a larger scale, more automated import, also considering land height, mountains etc.
There seems to be all ready 3D information encoded on open street maps, as well as a onlineand offline viewers for the 3D landscapes, its more of a question of importing it into Blender (and possibly also exporting some information back to osm in the future???)
I am currently trying to import one of these models to Blender manually just to see how it can go…
Nick