Eh for sure it can suck but also could get people more active. I have a product on our Vbulletin that permits users to set a predefined amount of posts to see a topic/section. It's pretty useful. And for the spam part? put a post limit for an amount of time for example: -10 posts = 5 posts minute. It works pretty well on my site and we got some useful moderators that also do the job against the spammers.