I don't see any reason to NOT allow guests to view certain forums, it's not like there's top secret information.
The teasers on the other hand might not be a bad idea, but I don't think there are really any "lurking" guests, mostly they just come for one page and leave.
However, there is a single thread that I constantly see guests viewing and new members viewing to download.
http://zelaron.com/forum/showthread.php?t=29948
Almost every new member we get goes to that thread to download the attachment, most likely because they cannot download it as a guest. Perhaps there is some way we can somehow funnel them into posting a bit, maybe make it where you have to be a member and make 10 posts before you can download attachments.
Oh, and the attachment says this "5312 views."
That's probably like 1000 times more than any other attachment on Zelaron.
Also, if you google "warcraft 1.15 maphack" we're the first link, and if you just google "warcraft maphack" we're number 4. We need to exploit this somehow.