I agree that incentivizing writers is the hard part about your site.

I assume the blog will be monetized with advertising. If so, have you thought about a revenue sharing agreement with your writers based on ad clicks? Sort of like Huffington post, but instead of paying the writers on articles submitted (or nothing at all), you could pay them a piece of the ad revenue they generate. Sites like squidoo.com and newsvine.com follow this model.

The revenue sharing article market appears crowded, but can turn out to be lucrative if you differentiate in some way (like gurufocus).