I also have a Bluetooth setup got my helmet. I used to listen when I ride.
Last summer the car in front of me slammed into the car that pulled out in front of it from a blind alley and went 40-0 in nothing flat. Even though I was following at a safe distance and had plenty of room to stop, I couldn't hear what was going on behind me because of the music (and wasn't turned up that loud). So I lightened up on the brakes, looked behind, saw that the truck behind me also had plenty of room (thankfully driven be a fellow rider) and returned my attention to the task at hand. By then, the car in front was much closer than I thought it would be. I grabbed a handful of brake and stopped millimeters off the bumper with my rear tire in the air. I lost my footing when I came back down and dropped the bike. Other than my ego I was unhurt; the bike had amazingly little damage. Not a spot on the fairings, but a bent brake lever and clipon set me back several hundred dollars.
All that said, while I can't say that absolutely the music being on made any difference, or that it would have happened any differently with in-helmet silence, its been off ever since. Just in case.
(As a side note, I enjoy the ride even more now and feel a little more in tune [pun intended] with the bike and the road.)