I planned to build a yard that would hold my favorite unit-trains (modern crude-oil, Railbox boxcars, FedEx spine-car, and a military consist), but I'm afraid the stubs won't be long enough. Plus I have a ton of passenger stuff. I also have way more locos that I can put on my layout (currently about 60 or so locos, and well over a 100 pieces of rolling stock). I also often forget what I actually have. Like someone said, it's a nice surprise to dig out older locos you forgotten about—it's like getting a new loco!
I like the idea of having a shelf of unpowered track, since I'm not too keen on either the display case approach, or the put-them-back-in-their box method. I have some Ikea shelving that I can use for that. I could even make some scenery on them to make like static dioramas; though, they'll really just be long shelves to hold my off-layout locos. It would be nice to fabricate some long Plexiglas covers to keep the dust off them, though.