but the level of activity you see in altcoin trading isn't consistent with other people pursuing that approach at all.
It sort of is. The Poloniex trollbox is absolutely clueless nowadays. There are people who believe "CasinoCoin" is a coin that will be adopted by casinos (lol). People exist who believe the propaganda spread by paid shills that claimed Ethereum is not only legit and not a scam, but better than Bitcoin itself (it's a pump and dump scam like all premines and fundamentally broken to boot). Individuals like Max Keiser wander in and pump Factcom to the moon as just a long shot gamble even though he has no idea if it's a viable system or not, which then attracts random noobs into thinking it might have value. Then day traders create charts off those movements, which creates volume and more traders who think, "well, this here potatocoin has millions in market cap, it must be legit!"