They did those boat condo's north of Havasu a few years back that are basically the same principal.. They even had a shower for people etc.. there.
I'm not sure how that ever panned out? I know Fast Timmy bought one, and a few others looked pretty hard at them. Maybe they can shed some light on them?
Honestly though, other then the cheap price (which in reality wouldn't be that cheap everywhere else) for owning a structure, I can't imagine them being some skyrocket investment. Then again I know shit about investments so it's just an opinion..
RD