I really think you could have something cool here if you focus on the aspect of sharing and discovering new content - Maybe a bit of a weird comment from someone who avoids facebook and twitter, but I'd say a huge benefit to your users would simply be providing ways for them to quickly get their stories read by new people.

In other words, users should be able to opt-in stories into a public feed of new stories, or stories by tag/type, so that others can come along and browse by recent or tag and find new content relevant to their interests. Clearly, things should also be able to be private, and likely should be private by default.

If the service had that, and didn't require me to use Facebook/Twitter, I'd consider signing up and putting up some of my own content, as one of my biggest hurdles has always been getting what I've written in front of a wider audience of readers, for the purpose of getting a more diverse collection of critiques.

Hope you keep at it!