Something like users must earn 5 merits a months for their account to display a signature if being done by theymos or managers can make a user earn 1 merit per week to stay in a campaign.
This idea is good, and suitable to apply for next campaigns with new rules from forum admin. I am waiting for this one. It will be better to restrict campaigns like this because it will help to eliminate accounts which have already stayed at higher ranks before the launch of merit system. Those ones should be prevent to join campaigns somehow, and your suggestion might be one of appropriate solution to control spamming-higher-rank users.