I started viewing this forum for the WTS/WTT ad's. But I can understand how you'd want to limit it. I posted a rifle for sale a while ago and on occasion still get e-mails from people stating "I ran across your ad google searching "blah blah blah". Are you willing to ship out of state????" when the ad in question is long gone.
Maybe just prevent people from PM'ing after 75 posts or so (if possible)? That way if people post their number/e-mail, they're asking for the minor annoyance.
I think you'd lose valuable new members if you restricted viewing of that sub forum all together. As like I said, those sub forums are what brought me to viewing this forum daily.