I think it would be fun to do something short term...might be a fun way to see the United States. But, I couldn't live that lifestyle, long term.
People talk about being trapped by big houses, luxury splurges, etc. But to me, something like living out of a van could become its own trap. If you have the money for something better, you can stop doing it and go home once the magic wears off. But to be forced to live on so little, I'd worry about what happened if the van broke down, where I might be spending my next night if I can't find a free/ultra-cheap place to park, where my next meal is coming from, etc.
I guess you'd get used to it, but to me it would seem like a life of constant worry.