I don't like this idea. Sure, abandoned structurally unsafe buildings should be torn down. Tearing down empty big box stores might not be a bad idea either, but tearing down usable homes and entire neighborhoods seems like very short-term thinking to me.
I've noticed that often poorer neighborhoods have some very nice old homes. We shouldn't be tearing them down, we should be restoring them. There's lots of historic architecture out there that helps give cities their character, and already too many beautiful buildings have been torn down to build CVSs and parking lots.
What happens when the economy does rebound and the demand for housing rises? The remaining housing will be costlier and developers will just go ahead and replace the demolished neighborhoods with expensive "luxury" apartments, condos and McMansions that people will need to take out expensive mortgages to afford. It will be the housing/mortgage bubble all over again.
We should be encouraging more people to move to cities. They're more environmentally sustainable then suburbs. If there's a glut of empty homes, we should be making home ownership easier and affordable, not tear them down.
Tearing down blocks of buildings to return them to nature might make city government accountants and narrow minded environmentalists happy, but it's really a wasted opportunity.