I don't want to ban people, I quite dislike it actually, I think everyone should be free to express themselves here with minimal restrictions. I've declined to ban people many times up to now for this, and I've been wracking my brain thinking of ways to deal with it without having to ban people. The longest running thread in the staff forum besides the ban request thread is a thread about the paid signature campaign and how to deal with it. It's a huge issue. This spam has to stop, people are making worthless post after post and drowning out good discussion with complete garbage and it's ruining this forum.
After this, they just upped their payments in order to attract more of the higher ranking members. And the risk? What risk? It's really hard to get banned here, you have to be a spambot or a complete idiot to get banned here. There is no risk, which makes this measure completely and utterly worthless, and that obviously isn't what theymos intended if you read that post. There needs to be some risk, and I'm going to make sure there is, or else I'm failing everyone on this forum in my duties as a moderator. I've made many posts with suggestions on how to fix this issue without having to resort to banning people, but in reality none of them really work without punishing everyone. I don't like that it's come to this, but it's necessary.
I think deleting the offending posts and/or messaging them a warning that if they continue to post crap at their current rate they will be banned will be a stern enough warning. If they're having their posts actually deleted then this will obviously make them step up their content as it's not worth it to them and is actually counter-productive to keep doing so. If after a warning they continue to act the same then give them a weeks ban as punishment and then they should get the idea. Like you said, many don't want to risk their accounts as they are valuable to them so banning outright, especially without a warning (if you didn't give them any other warning), should be a last resort and could probably be avoided in most cases.