Well, yeah, but it would give them an incentive to invest more in targeting their customers correctly. At this point, a million new addresses to a spammer is an asset; if we implemented this plan, that would be a huge liability.

The ideal, once your email-receiving price gets high enough, would be for spammers to basically send the kind of spam that you would have paid to know about anyway (e.g. instead of reading a gadget blog, spammer pays you $1 to look at his customized spiel pitching a particular gadget similar to the ones you've previously liked).