It seems like you've got everything needed for a thriving marketplace without the market.
Why is your content all free? Have you tried to directly monetize the content? Why not have the first x,xxx downloads free, then monetize the content and split revenue with the author & publisher? Or have a graduated cost based on popularity, similar to what pinboard did? Something like this may have the side benefit of creating a sense of urgency and anticipation for your newsletter.
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