Welcome to the site. You've met Tim, who'll generally answer you in what many people view to be an insensitive manner.
Unfortunately, he's invariably right, so I'll dance around in a slightly more subtle and verbose way, or you could just re-read his comment to save yourself some time, on the other hand.
I've 8 years experience founding and running my own company and completed an MBA before that. I can safely say in retrospect the MBA is worth SFA compared to the experience. So I'm hoping that you can add a good number of years of combined startup experience to your qualifications?
Ultimately, there are two things adding value in your model, the startups and the mentors. Your role, as I understand it, is getting these two together. The problem is that a number of companies and organizations already attempt this. I personally think that a goodly amount of research by both parties would perform this task and doubt the value of a dating site for startups.
The place that a lot of mentors fit in is at initial funding, the mentors are linked to the funds. Obviously, your problem is lack of track record (which is why you're asking).
I don't see any USP over anyone else in this market. I'd suggest picking a specific niche of startup type and specialising in that. Then later expand into other vertical domains, but keeping the same focus within each one, to give both parties the feeling you're expert in this role for that field.