Most of us will fail in this task. Suppose, for example, that the members who participate in the signature campaigns are 500 members, and with restrictions of about 20 Merits per month, this means 10K merits per month.
20 merits a month is going overboard and even 10 sounds like way too much.
You say it's easy for 500 members to get 20 merits a month but I doubt there are that many posters overall in the gambling section that get that many, probably one of our AI friends might come up with a list but I'm betting that there are way fewer users that get 20 a month and that there is way less merit being spent on the gambling board than other subforums, so a higher requirement will also hurt some that don't frequent high merit distribution areas too.
I think we're slowly turning from making the board less spammy to making it some sort of restricted area for older users only.