You've said it better than I ever could have.
Musk is trying to demonstrate that the entire valuation system for companies is broken.
WalMart is successful because they pay people less than a living wage, and the government picks up the slack.
The entire assets and future of Tesla is not now, and never will be, worth $420 a share. But the idea of Tesla? The goals of Tesla/Musk? I'll buy that shit at $1000 and be pleased as fucking punch to have a tiny a part in it.
I think Musk's whole idea is to destroy Wall Street and the rapacious culture of "profits over people", and force people to weigh the entire benefit/impact of a company and their products and culture, rather than solely basing value on quarterly earnings.