As Daniel mentioned modularity is potentially a good way to go. A really good tutorial series on 3Dmotive explains and demonstrates the benefits and workflow for using “Lego” pieces to build your buildings. This is something that Epic and a lot of other developers use in their games!
3DMotive Modular Building series
One of our senior artists, Kevin Johnstone, has a great power point he used for the East Coast Games Conference here in Raleigh, NC a couple of years ago. This will give you some key points about modularity and using the grid to your benefit in Max and UE4. Check out his site here.
In regards to modeling everything being a time sink, this is absolutely true! It’s easy to have it become that way. As you work you’ll get a workflow that works best for you and getting the work done!
If you have any questions feel free to ask!