One of the major problems Stackexchange sites have(after the initial population, it is of course a huge advantage to begin with) is that the major pool of users for each site comes from the stackexchange network namely the big IT related three SO SU SF.
Obviously not all of these users are musicians, nor do all of them have time to be on bicycles.se, skeptics.se, homebrew.se, music.se stackoverflow, etcetera and still have enough time to pursue the real life interests/hobbies they are asking questions about.
You need to get users from outside the stackexchange network. The problem with getting users from outside the stackexchange network is that they are not schooled in the stackexchange mode of operation. Also for topics such as music/the arts, musically creative people tend to be less rigid and if they don't have the IT/SO background overly-zealous moderation may be an off putter to them.
I think moderation of SE sites like music.se should take this into consideration with new users, and at least try and edit new users questions or guide them before just blankly closing them. We want users to feel like they can interact when they get here, so they should be handled with kid gloves initially, until they learn the ropes.
I believe that this will help the site grow and be more accessible to any new users that come here.
I also think that designing and applying a style to music.se (al la gaming.se - photography.se), will give the site more of an individual character, which may make a difference.