The simple solution to the problem is to disable the meriting of WO posts. Much like how signatures were disabled in that thread, it will discourage spammers from flooding the thread.
Disabling of merits on that thread will be an injustice to the senior and most well known members who have been active on that thread for a long time. Some of those members don't post on other threads at all, and if merits are disabled on that thread then their accounts may also not get new merits. That's actually not a problem because those members really don't need or care about merits that much because as far as I have noticed that none of them is in a signature campaign and they don't really care about signature campaigns at all.
The most members of the thread are true Bitcoin enthusiasts and they love to spend their time on that thread, and whenever they see a good post on that thread they can't stop themselves from sending merits to those posts. I think nothing is wrong in that kind of merit sending and the ones who are basically there for merit fishing won't get any better even if they receive 1000 merits which are required for legendary rank. I don't think that any manager would accept such merit fishers in their campaigns because most of the managers want high quality posters who could create useful posts for promotion of a campaign.