I think that by offering a members for sale option on a freebie basis would provide for increased site traffic generation. Advertsing is as much a part of the site as is the editorial and a good "classified" section will bring people back to the site thus creating a regular viewership which in turn will impact on upon "dispaly" ad. sales - banners, pop ups and additional promotions. I don't know how you are measuring your site traffic - web trends? Red Sherrif?
I am involved in new media but use this site out of personal interest and see an advantage in having a "members only" ad. forum which generates regualr traffic to attract the brand advertisers at a premium rate. Punters are not yet ready to pay for content in any great numbers, therefore you need to not only generate site traffic, but also keep up and build on regular readers - oddly enough not dissimilar to what you had to achieve in print! Some may say that this is heresy but its a fact of life, advertsing, sponsorship etc does make the world go round!