I do agree with OP about increasing number of participants, also I do believe they're mostly multi-account. But about earnings, I dont agree at all, there are many bounty campaign outside bitcointalk which get less attention from bounty hunters and they're still worth to join.
Yeah, it will be on us how we will earn from it, many bounty participants can minimize the earnings but might be a scam project. It will depend on how we will choose it. It doesn't matter if here in bitcointalk or outside of it. The project or coin will matter it.