It's a nice thought; I'm not seeing a lot of traffic though.
Might I suggest a refinement? "Models" is a bit broad - I started a subcategory (http://www.thingiverse.com/groups/toy-replacement-bits/things right before I found this - didn't mean to undermine), and I'm encouraging visitors to both post what they Have but would otherwise be ashamed to post ("I got a lightsaber and calipers but I'm no good with 3D modeling, anyone need the dimensions on it?") to at least get the ball rolling; I figure there's probably a lot of people that have half of the solution, if we can get everyone together we can accomplish a lot, yeah?
I mean, I expect a lot of people are glancing through, seeing something doesn't exist, and giving up.