Looking at the board stats I see hundreds of visitors lurking about and not logging in
From all my years of forum management, I've noticed a lot of guests constantly online as well. This puzzled me for the longest time as it seemed like forums were busier than they really were, but they weren't.
You should look into options to see who the guests are to determine which path to take as this way may have a dismal unseen future effect.
Usually, the guests are bots that are in the process of spidering the website which leads to ranking for keywords that drive real visitors. Having disabled viewing of threads for everyone has the implication of ruining the established ranks that you already have and will eventually make DN.ca fall from all search engine results because there's "nothing of value here" (that the search engines, or bots, that you blocked can see).
One thing to consider is allowing guests the option to post, with manual reviewing of course, and then later converting those posts from guests to members. Another could be letting the bots through but denying the real visitors access or denying them access after X page viewes. You could also open up one section of the forum just for some rankings.
I can't delve too deep into options that will help -- over hindering natural forum growth -- as I am unfamiliar with the tools you have at your disposal.
I'd love to help more, but I kind of have a 'no compete' (as I'm building a forum network to hopefully, one day, rival VerticalScope) and it would also be a conflict of interest. But, I hope this reaches you well!