Looks like you're right All Electric Tesla Roadster Driving from L.A. to Detroit | Earthtechling VIN #1000 was displayed there as well and looks like it was sold for charity http://www.theautochannel.com/news/2010/01/12/461509.html
I think they drove #750 across country to the Detroit Auto Show where it met up with #1000. Basically #750 was displayed as a dirty example that Roadsters are real world cars meant to be driven, and #1000 was shown off in its' pristine, detailed glory. I think #1000 was made soon after #750, but they skipped forward a bunch of VINs so they could commemorate the "1000th Roadster." (But that probably took into account EPs, VPs, Founders, and some European Roadsters, so they doled out North American VIN#1000 a bit early.)
Old pictures: 2010 Detroit - Proceeds from Sale of Tesla Roadster No. 1000 Goes to Charity Tesla Roadster #1000: Tesla Roadster #750:
More old pictures of #750 here: Picasa Web Albums - Bob - Tesla Roadster (Dec 28, 2009 - Dallas, TX) "750" Tesla Roadster Now in Texas...
Slightly OT but... The prototype's side mirrors don't look (vertically) symmetrical in this picture like they do in every other picture that I recall.
That was the original concept car, so it had a LOT of differences from later alphas/betas/production models. See the mirror here: (I think it was originally gray, but got damaged in shipping, so they repainted it in a Signature Red like color.)