I believe you are on to something here.  Proof-of-scam can actually be argued as a reason for making a speculative purchase in an alt-coin.  A speculator buys in just for the hype--he doesn't drink the "this-will-be-the-next-bitcoin" koolaid--and he plans to trade back into bitcoin before the bubble is over.  

If this theory turns out to be empirically true, I think it adds more evidence to the notion that all alt-coins will eventually die as the life-and-death cycle of altcoins becomes more clear.  According to your proof-of-scam theory, since the scamcoins have the greatest chance of being pumped (and later dumped), there is less interest in non-scamcoins because their is little incentive to pump them in the first place.  

Personally, I support the spin-off mechanism for launching new experimental alt-coins.  Bootstrapping the coin with a Blockchain-based initial coin distribution makes it more difficult to pump and dump, and automatically piggybacks all bitcoin holders to any real innovations in cryptocurrency.  Spin-offs allow for innovation without threatening the wealth encoded in the Blockchain Ledger