I think two relatively simple rules will eliminate a lot of the chaff and spam without impacting the 'sensible off-topicness':
1) you need to be Hero or Legendary member or member joined before 2014 to post in WO
2) posts in WO do not add to a poster's Activity Count
This will essentially make it somewhat exclusive for posters who have already earned their stripes elsewhere in the forum, i.e. veterans. And it reflects the make-up and effective purposeful useage of the thread as it stands, long-time posters who are occasionally or regularly checking in on this thread,posting price news, thoughts opinions and sometimes loosely related bitcoin or personal material.
The spamming and attempts at disruption are usually from new accounts who covet the attention provided by the thread. Bashing the Off-topic button seems to be their latest tactic, since that is how they have been shut-out most recently (classic DDOS attack is to exhaust the most effective defence). People might not know of the huge job Lauda has done in the past cleaning up after NotLambChop and shutting out that entity's attack on the WO. The current Off-topic attack is most likely a response to that ... there has probably been collateral damage and Lauda has collected some undeserved ill-will for that previous defence.
NB: I'm not available to mod WO ... but I think you need to get it sorted out quickly, it's not that big of deal if you enforce those two simple rules above you could even put a drunk and his monkey in charge.

The idea of "exclusive" is fairly intriguing, and would likely take a way a lot of the problems - including taxation of moderation - even though there may still be some bought accounts or some of those kinds of possible shills that would come about from time to time.. but likely a lot more rarely with the more senior accounts.
Personally, I am of the inclination that if the WO thread were Full member and above, then there would need to be few other restrictions - and then who ever is the moderator would be quite a bit less taxed, and could exercise discretion when s/he thinks that posters have gone too far... which likely not be very common... and almost as if we wouldn't need a moderator in such circumstances... except these more extreme situations.
In other words, if we go in the exclusive direction, I would suggest either member or Full member and above (and leaning more towards Full member and above)... for participation and voting rights in the thread or related to the thread.