I agree with Forester1 on this. When I've put together cities, I ensure they look busy and built up from the distance but not overly huge and eating up a lot of resources and focus my efforts closer to the tracks. If I want to fill in areas with buildings, I use the old Cityscape series blocks by Dave Drake (dmdrake). There are a number of these on the DLS. They have names such as Brooklyn, and so on, but they're generic city blocks with a bunch of his buildings setup in squares. Putting a bunch of these close together and then putting mode detailed buildings in the front with fences and what not usually does the trick.
For real though, we can go nuts building cities with the infinite details and in the end it's a lot of extra effort depending on the purpose of the route and also even with today's computers with their faster video cards, CPUs and gobs of RAM, this is still a resource hit when it comes to performance when setup with large goods yards, passenger terminals, and all those other details we want close to the tracks.