SteamDB gives a value of 2500€, 9500€ if I bought everything with today's prices, for my library, most of which are from Humble Bundle, and I have probably 150 unredeemed keys as well. I could easily sell 95% of them as I've played through them or don't like them, and net a sizeable profit in the process. And I'm definitely not alone.

They would have to implement some sort of revenue sharing for sure that guaranteed some of the resell value went back to the developer, or this would indeed be the result. Also all bundle/discount sites would die overnight anyway.