Perhaps the answer could be making sure signature campaigners do not post vague stuff is the responsibility of the bounty managers. And even if EVERY post was made to be productive, there would still be too many posters. So I think the issue is either setting stricter signature campaign limits or by setting stricter regulations on who is allowed to advertise/join such campaigns and how they should conduct said campaigns.
But a few moderators might also solve the problem, as you said.
We've been advocating that for years, but ultimately a lot of signature campaigns are gambling related, and therefore they want their posts in that section. I doubt the forum is going to enforce rules/guidelines specifically for signature campaigns, if theymos does decide to address the issues caused by it, I imagine it would be less restrictions, and more just outright banning it. Although, theymos has expressed in the past that he likes that signature campaigns have created an economy within the forum. So, I imagine it would be with reluctance, and I don't think the signature campaigns are our biggest problem right now.
Bounties on the other hand are still a problem, despite theymos' efforts with the bumping changes.