After a month of extreme work on SongBox I've had my second person sign up to paid plan in a week.
Interestingly, this person was one of my first signups from well over a year ago. Looks like the recent improvements have convinced to not only come back to SongBox, but to pay $80 for a yearly PRO plan.
Two paid members in a week with very little marketing spend.
I'm more convinced than ever that SongBox has legs.