While I can sympathize with the core of your argument, as it stands now we have always had people posting tons of no-content stuff (both threads and posts) for no reason at all. If there were more moderation on the forum, or the forum's populace showed more restraint and better judgment, it wouldn't be an issue. In the main discussion forum, DwarfMeister basically posted 7 or so threads in the span of two days, flooding the first and second pages with whatever popped into their head.
I'm a fan of SA's rule of "don't post anything unless it's funny or adds something new to the discussion" as well as "hang out a while and read before you start posting". I'm very much in favor of better discussion rather than 'more' discussion.
Considering that there are thousands of active forum members, with around 100-300 on at any given time, at some point something's going to have to be done to keep the community from spiraling into utter trash, like the Blizzard, Mojang, or [insert other popular game here] forums.
Edit: To make sure this stays somewhat on topic, I know Toady has been concerned about adbots for a while. I know he's tried to finesse the registration process once or twice to keep 'em out, but obviously that hasn't worked so well.