I'm not the best person to ask but I believe it helps a lot! How much signal it adds, relative to others, I couldn't say. But obviously they should mention it in their application.
The ability to make something people want is so central to what YC is looking for that it's the company motto; and sooner or later "want" has to mean "want enough to pay for". Sounds like your friends are already there.
The ability to make something people want is so central to what YC is looking for that it's the company motto; and sooner or later "want" has to mean "want enough to pay for". Sounds like your friends are already there.