That sounds like fun. I originally wanted to attend one concert near NYC and then use Amtrak to catch the DC concert the next day. I should have done it (it wouldn't have cost me more than an additional $150).
And the region from NYC through Pholadelphia, Baltimore and then DC is all reasonably accessible via train or bus.
Makes it easier to get around. Transport isn't always as affordable as some European destinations. And lodging...well your sleeping bad in the Park makes sense to me because the price of a "cheap" NYC hotel room isn't good and it was probably safer.
Oh and the fixation on empty containers, great "revenue enhancer", isn't it?