There are a ton of companies that don't achieve venture scale and end up going away. Often times this leaves a void in the marketplace where value was once provided.
What are your thoughts on taking old, VC tested/failed ideas and trying them again? The only difference in this new scenario is that instead of taking outside funding, bootstrap the company and grow at a sustainable pace.
Given that, yeah, I think "failed" ideas are a gold-mine of potential. The big question, of course, is "can you identify the ones that are fundamentally good, and just need a little polish or maybe a tweak to the business model, from the ones that are just plain wrong?" And if so, can you come up with the little extra mojo that would allow that idea to be brought back, and become successful? If so, then you are probably onto something.
FWIW, I spend a fair amount of time looking at old ideas (not specifically ones involving failed VC backed companies though), always thinking in terms of "is there something here that can be re-invented, re-mixed, re-purposed, etc?" I can't claim any major successes yet, but I have a few things "in my hip pocket" that I hope to get too eventually.
Anyway, I say "go for it."