Blender render eh? Click on the light, then go to object data, scroll down to the sampling section and set both a high sampling rate and smooth shadows. Instant render improvement
Your car model is pretty decent. I recently did a Ford Interceptor using nothing but tracing paths. How did you go about your model? One video tutorial I saw built his car using nothing but a single cube. It was quite intriguing.
I would consider putting in a little extra detail to the buildings rather than vanilla texturing them. Even GTA IV had a lot of useless buildings, but they added some extrusions typically at the doorways and stairwells to add some dimension.
Anything else you care to share about your WIP? What engine you're using, does it tie in with Blender, how far along are you, etc.?