I've seen the math done on the unused IPv4 space by some institutions. In the end, even if an organization gave up their entire /8, you get something like 1 to 2 months of extra time at best.
Only one or two months, yes, because there's an allocation problem. Unless that's fixed (and it won't be), just giving back extra addresses will only result in them being squandered ... again.
That is still allocations, not usage. If we had a public market for IPv4 addresses there would be incentive to use them like the limited resource they are.
I wouldn't doubt it. I suppose it comes down more to personal opinions at some point, but I'd rather see an Internet of mass availability and resources. I can start a web service from my house because I can rent a VPS (including IP) for a few $'s per month.