Thanks everybody. They pretty much let me do anything I want here in my office. I've got my own artwork up on the walls as well, cause the corporate stuff is JUNK.
The diorama measures 5" x 49"; in my move to a new office, turns out I could add another 10" if I so choose (bigger credenza behind me now). I'm gonna use it just to display newer units, but not my *best* units (i.e., nothing higher than an Athearn) - we've had a lot of thievery recently here at the college. A couple of my coworkers at least like to poke their heads in whenever I've got new units and take a look.
I'm going to leave it here at the office, it's fun to display different units, and the NorQuest Express loco of course (that's where I work, see below). I hadn't thought of a backdrop, but that would be an easy addition.
If I did add another 10", I'm not sure what it would be either - I've got plenty of space on the credenza, so maybe even a small industrial building, jutting outwards in the corner.
I've got the top of a file cabinet free too, so I might build another diorama for there with the Medusa Cement facility (this would only be temporary, as it will be moved to the layout once ready). I could put the two ROCK switchers there, they would look pretty kewl, and I'm working on my third two-bay ROCK covered hopper, all of which would look pretty kewl in front of the cement facility. This could be as large as 18" x 36", and just keep it firmly attached with some doublesided tape until it needs to go home.