Maybe there were less pointless posts. But I wouldn't take it for granted.
There are many forums where people don't get paid, have a lot of traffic and a lot of pointless posts, like this one:
https://forocoches.com/Would it be less filled with spams?
Not sure. On one hand if you take away the incentive to frequently post, there would be less meaningless topics and replies, which reproduce themselves, but on the other hand, you would also take away legitimate users who do help (and don't have the time to do it voluntarily obviously). Check topics from 2012-14, when there weren't signature campaigns, and tell me if you'd rather have that. I wouldn't. They are dead posts, and there's barely a constructive one.
Like the forum I mentioned. I agree that getting paid for writing is a double-edged sword, on the one hand you incentivise low quality posts but on the other hand you also incentivise constructive and high quality posts. I think with the introduction of the merit system the spam problem was reduced quite a bit, although it was not completely eliminated but it's pretty good for what it was in 2017 or 2018. Wanting to get rid of low quality conversations on forums and at the same time maintain good traffic seems to me to be an oxymoron.