Boycotting - a posting freeze - would work perfectly. BUT, the hard part is getting people to comply to it. You'd risk giving your spot up for some person just joining that wants in, but at least you'd have stuck to your principles! And of course all the vet bitcointalkers that hate the volume the signature campaigns bring would be thrilled!
You should give it a shot!
If you are confident about your posts you won't have a problem. Because there are too many users but only few quality posters. Campaign managers will select better users for their limited places. Don't forget it's all about how you advertise your product. Companies don't want some shit-posters to advertise their product/site when they have a choice to pick only elite posters.