It's a tough situation. On one hand, it is great that this community has decentralized sources providing revenue to it's users. On the other hand, those decentralized sources are being highly manipulated by established members and their armies of alts to spam the forum and collect all available revenue.
I honestly don't see any remedy for the situation outside of centralizing signature campaigns and having the forum be responsible for their displays and payouts. While I'm sure this would be profitable for the forum, I don't think it aligns with the theme here. It would also put signature managers out of business, who are in my opinion the ones to blame for the spam problems here. That would surely have an effect on forum views and perhaps even a longterm negative effect on profits.
The spam problem can seem insurmountable but it is not. As you suggest, this would be a non-issue in a centralized system. This is something we should not hurry into. There is already glimmers of hope as over time, the forum is evolving its own defense mechanisms; its immune system, aided by a few vaccination doses from Theymos and admins. People like us who care and those who fight actively like the pharmacist, hilarious etc are like the White blood cells of this organism..
An example of this evolution is the easy to spot newbie/jr.member with "one-line" generic shitposts and the "nested reports". Like the common cold and flu, these are easy to spot symptoms. I have been trying to find people to merit. While doing that, I couldn't bring myself to merit post histories filled with these reports or these one-liners. Most people giving out merit may feel this way and such users will never get merit. The participants will in turn, avoid campaigns that need such nested reports. As people would be unwilling to join such campaigns, either the practice will stop or the pathogens will evolve. Like everything else in life, It is going to be a constant fight to keep the forum in good shape.