It's easy to pretend we don't do anything because you don't see it, but reality is we do quite a lot.
The work you do is appreciated but still I see "pointless post after pointless post" that are basically no better than the old +1's generally with PrimeDice in their sig (the number one sponsor of useless posts on this forum IMO).
Maybe the sponsor should be banned (then they might be more picky about who they let post for them)?
Perhaps also sigs could be limited to not appear in any "useful boards" (that way they useless posters can just post in useless boards such as Lending).
We actually ended paying per post count two days ago, I agree it definitely was watering down the quality of posts on this forum to a drastic degree. For anyone wondering we honestly did try hard to prevent spam in the campaign with last round reduced down to senior/hero members only and half of the seniors cut out but when the incentive to post is so high, spam is impossible to prevent. I still feel bad for popularizing this disruptive form of advertisement.
If you want this issue to be solved entirely it's simple, you just ban campaigns that pay per post. If you are paying a fixed amount for advertising depending on a user's rank then there is no reason to believe spam would increase as a result.
It's important to also make it more difficult to evade bans and outright ban the sale of accounts.
If you would stop paying someone .001 BTC for every post up to 400 posts per month then users would not want to try to post 400 posts per month.
If you are paying users a fixed rate (say .1 per month) for a minimum number of posts (say 50) then you are still paying on a per post basis, only that you will pay more per post and pay for less overall posts. The result is that users would make 50 posts (in my example) and then stop. "banning" pay per post signature campaigns will not stop anything. The only way to get completely away from "pay per post" is to pay users a fixed amount regardless of how much they post during that payment period.
The fact is that paid signatures allow for bitcoin related businesses to grow, which will allow the overall bitcoin economy to grow.
I do agree with evilpanda that there is a significant amount of spam from newer members without any kind of signature for
reasons. I am not sure if these posts would qualify as the forum's definition of "spam" but I have scrolled past pages of one sentence posts that really have nothing that can be replied to in any way. When you have a paid signature, if your posts are insubstantial enough then the campaign operator may not pay that user, so they have a disincentive to outright spam, this risk is not present for people without signatures. If a campaign operator does not police the quality of their users' posts then the advertising will not be as effective.
It should also be understood that a single answer in a newbie thread will (should) not be considered to be credible to the newbie regardless of it's accuracy. If someone is a newbie, then they do not know who to trust and a scammer could potentially say something that "sounds good" or "sounds right" but is not. If multiple people respond with the general same answer then such answer would have somewhat higher level of legitimacy.
I do think that many people with paid signatures would likely not be here if it were not for the paid signature (nor would they be interested in or use bitcoin). Having a paid signature does give some people the incentive to learn about (and ultimately use) bitcoin. I think this fact outweighs the negative effects of the (IMO small amount of) additional spam that results from paid signatures.