I think I've seen something about the hair/wish thing before. Once or twice? In the context of how many things I've actually read though, that's basically a reference that barely exists at that point. A whisper of a ghost. Much more commonly seen would be mention of the 100 shrine visits thing.It's kinda like when you set a big goal while growing your hair out until that goal is achieved. I suppose it's to show determination and Maya probably does it to encourage Mameyama (in a superstitious way).
Sorry if I worded it badly lol.