In effect, we see a closely-knit expert group with a very high bar for joining, which merely uses a forum with a much wider membership base as its communication medium... most of what actually happens here is sheer dead weight, imposed by the open nature of the forum that is inherently in conflict with such goals.

I'd say the bar for joining isn't very high (you only have to know the right kind of undergraduate math, a lot of which was even covered on LW), and the open forum is also useful for recruiting new members into the "group", not just communication. Everytime I post some rigorous argument, I hope to interest more people than just the "regulars" into advancing it further.