In other words how many of you out there would have believed in the concept alone and worked for equity?
If the idea was pitched by Evan Spiegel, I would have most likely take it up. For me the team is more important than the idea itself.
As with all things, it depends. Part is about if you would use it. That covers your excitement about the project that makes it easier. Second is if you can afford to work for nothing if it blows up. As an aside, several analysts question if Snap will actually get public because of the FB competition. So, like any religious experience, you have to believe in the mission in the face of no proof, only faith. Age is an issue. The younger you are the more you can afford a failure. Experience is a factor because when you have no resume you need it; when you have had successful projects and exits, you can be more selectiv.
I think it's actually not the concept alone you need to believe in, but mainly the capabilities of the "business people" to win the first (and most difficult) 20-50.000 users. If you believe that, you evaluate the concept.