Like tbowman said, you need to go through the customer discovery phase and build up a solid amount of feedback from your target market. Read the Lean Startup and any of Steve Blank's customer development books / essays. Check out Ash Maurya's Lean Canvas as well - those 3 resources will give you a roadmap to follow.
If you've talked to 20 - 30 people and they are giving you really good feedback already, that's great because it sounds like you're on the right path. 20 - 30 is not really enough to be truly representative though, so you should aim to interview around 200 people from your target market, which can be quite a daunting process.
There are platforms like Instant.ly that will gather large amounts of data from a target market for you (although it's quite expensive). I recently saw a great interview with the founder of LikeBright, he used mTurk to set up phone interviews with his target market, although obviously if you have a niche product mTurk doesn't really allow you to drill down to a specific TM.
So yeah, aim for 200 people from your target market, and be prepared to pay for it, or spend time setting up interviews yourself. Good feedback from a large number of your TM will put you in a good position to approach an incubator or seed investor (oh yeah, check out Angel List as well:)