We already have a pretty comprehensive set of rules for both campaign managers and participants here: Signature Campaign Guidelines (read this before starting or joining a campaign).

This sticky gives very clear guidelines for what is considered spam, and what bans will be handed out to signature spammers. It also gives very clear guidelines that managers should be monitoring their participants, and campaigns which don't do this will also be banned. The problem is that these rules are going completely unenforced, and without some clear direction from theymos on this issue plus probably several new mods, this will continue to be the case.

I think this would need a considerable amount of work to start with, but would settle down relatively quickly. Once word starts spreading among the bad managers and users that both users and campaigns were being rapidly banned for spamming, I suspect they would quickly clean up their act.

I agree with many of the points above that enforcing some sort of minimum wage does little to address the underlying problem, and is mostly an unworkable solution.