If signature campaign is banned, spam will reduce but some good posters will also leave the forum or become not really active again.
That's it, and the next question is why are those services still interested in advertising here, even with minimal banner formats and thousands of dollars per week?
Beyond just analyzing visitor traffic, they know that this forum is active in almost every board. They don't care about spam or forum' purpose at all; they care about impressions. Their target audience isn't limited to technical experts; spammers might also be potential customers, contributing bigger revenue.
I suspect the threads that will remain active after the spam policy upgrade are:
https://bta.lk/t/5132720 and
https://bta.lk/t/1306983, and guess what, they'll attract advertisers? I've been on several older forums, including xdaforums (formerly xda-developers), where there's no spam, no drama, no incentives. Sometimes you have to wait hours to see a reply after yours is in the most popular section, and then days to get a new thread.
I don't support spam, however. If my previous suggestion is too harsh, I think we can at least utilize the report button and consider merit spending as strictly as possible. It would distribute responsibility to all constructive users instead of just merit sources.