My first thoughts about monetization: 1) allow people to sign up for catalogs too. I know that sounds insane to you, but I think a lot of people woul like a place to go to get stuff from stores and categories they like. That's easily monetized with the vendors themselves as part of their customer acquisition cost.

2) Even if you just stuck to removing from lists, you're actually providing value to the the direct mailers. They have one less printing and postage item cost that would have either been useless or pissed someone off. That could be over a dollar per household saved with each mailing.