Of course, the forum should put restrictions for users who are spamming this place. But making a rule in general for all members is not right in my opinion. I mean why punish all members for the spam caused by a handful of a members.
In my opinion, the limit to create certain number of threads in a day should be there. Usually , on small forums the staff is able to notice themselves if some user does this. But there is so much activity here, that is it almost impossible to spot all such users manually. If possible, reports should be sent to the staff once a member crosses that number of posts in certain time frame to check this.