Re: What would you pay??
Personally, I wouldn't pay for the discussion forum > I believe that while this isn't a 'free public forum' in the true sense of the open discussion forums, places like DW, where it's essentially the free exchange of ideas, is important and vital to community building. I suspect that if there were to be a user charge here; a great number of members would filter off elsewhere.
That being said - the aspect I would seriously consider paying for is access to the videos and educational material offered on the DW site. This aspect has definite value to me and my students and I never take it's availability for granted.