Personally, I prefer the idea of keeping the majority of the WW&F discussion forum open to anyone interested in the WW&F, regardless of membership in the museum. I know I became interested in the WW&F by following the frequent progress postings that James releases quarterly on the main web site... long before I became a member or active volunteer. (I suspect many of us share a similar story.) I consider the Discussion Forum an extension of this very effective "PR" tool among railroad hobbyists, enthusiasts, historians, modelers, etc.
That having been said, I would certainly be in favor of creating a new section (or restricting a current one) such that its contents can only be viewed by current members of the WW&F museum. This would be considered one of the benefits of being an active member of the WW&F Museum.
As Jason noted, there is a discussion starting about this amongst the BOD members. I await their decision and will set things up in whatever configuration they deem appropriate (if any.)
-Ed Lecuyer
WW&F Discussion Forum Moderator
(Who does not speak for the WW&F BOD in any way.)