I think it really depends if you think this is generating you more fans than it could be loosing. How have hits on this site increased since you started posting Warbreaker chapters? I know for me, a newcomer, these chapters mean that I'm often on this site. It's how I found out about the Mistborn pre-release, and now I'm bringing a friend. I wouldn't discount your agent out of hand (no one likes that), but weigh costs and benefits.
I think it's also unlikely that this will be the first work of yours that someone reads. I only found this forum through your website, and the first thing I did there was read Mistborn sample chapters. Then I began exploring, wanting more.
Personally, I really like being able to read the Warbreaker chapters. It's something I've never seen an author do before. It's exciting to read a book as it's written, before it's published (the really good story doesn't hurt, either), and exciting for me as a would-be-author to see a book developing from an author I respect.
I don't know if that was helpful, but as one of the new people here, I thought I'd offer a perspective from one of the masses who found out about this forum the way another potential reader might.