The reason I come to this forum is because I can usually find the information I need without having to wade through a bunch of spammy posts. I know of another site that allows links in the posts, signature links, etc. that has a huge following...but nearly useless information because the forum is full of people promoting their own stuff instead of people gathering to solve problems. With that said, I go to the spammy forum because I can promote my stuff. I come here when I need good quality information.
Bottom line, you have to decide if you want more visitors or if you want a quality site.