1.) Creating a filter system that finely discriminates between similar conditions (i.e. many ailments have very similar external symptoms, how will you distinguish between them?), but don't make it overly complex with a million options because people will get confused
2.) A novel rating system that can eliminate bad suggestions and bring to the top the most effective solutions (perhaps individuals who contribute some of the most effective treatments gain special status??)
3.) Personal picture and video submissions may be helpful, but always hold peoples' privacy with utmost regard; also, should you choose to incorporate multimedia into your site, do so with caution as I personally would not be so inclined to visit your site if I were greeted with throbbing pustules every which way!
This is an idea I (along with thousands of people I'm sure) have thought about. WebMD isn't bad but it can definitely be better.
If you want someone to bounce additional ideas off of let me know!