I think that learning to play a musical instrument would certainly help you with counting and phrasing, but I don't think it's the most efficient way to do it. If you want to learn to play an instrument anyway, go for it, it will be helpful. But if the only reason you want to play is to improve your sense of rhythm, I think there are better ways to do it. You'll spend an awful lot of time learning to read music and learning the mechanics of the instrument. If what you want to do is learn to move in time to music, I think your time will be better spent in activities where you do just that - in other words, more dance classes. It's no secret I'm a big fan of ballet for skaters, but I think many dance disciplines would do the job. Personally, I cross train in ballroom, and am finding it very beneficial.