I agree with both of James' comments (and can't really think of a time I haven't agreed with him, come to think of it).
However a lot of the value for me personally is in the forums helping me stay in a Mustachian mindset as I read and comment on posts, getting encouraged by other people's successes, occasionally getting a chance to help someone with some knowledge or bit they might not have thought of, and learning things when other people post things I didn't know myself.
Naturally, as one learns more, there will be diminishing returns on that last one, which is (selfishly) one of the best ones, but the other ones remain valid and useful, for me at the very least.
It's disappointing when an (otherwise perfectly valid) love for debate and search for proof gets in the way of actually learning stuff.
It only gets in the way when one lets it. Easy enough to avoid/ignore/move on when something is impeding you.
In the multiple threads that spawned from the one James' linked to, I think I commented once (obviously rare, for me on a forum). However I did read every post. I revised my thinking on some things, bit my tongue on some things, etc. Easy to take what I can from it, move on from some, and not let it impede my journey.
IMO, YMMV.