SEO benefit

[kl0000]

My online shop includes a small but growing system of of forums, one of which is a "member's lounge" for off-topic discussion, jokes, links, and so on. Currently it is accessible to registered members only; others (including search engine spiders) don't see it.

I've been thinking that if I allow non-members (including spiders) to access that off-topic forum, I might gain some small search engine benefit due to having an additional 1000+ pages indexed. (Right now I have 28,800 pages indexed in Google, and 24,500 in Yahoo.) All of these pages link back to the home page and other relevant site areas.

But on the other hand, apart from the navigation links, most of those pages aren't even remotely related to the rest of my site, or to any search terms I'm interested in. I know that linking to irrelevant pages is a bad thing; is linking from irrelevant pages, or simply having those pages on your domain, also a bad thing?

Any answers or insights are much appreciated!
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[Monnterella]

I think that it worth include. I believe that you will lose absolutely nothing with that.