The "on your left" thing doesn't really work when the person you're talking to can't hear you. I've had a different experience - riding frequently on the heavily used Los Gatos Creek Trail, I have many times encountered joggers, sometimes with strollers, who give no response to my signaling that I want to pass - and then when I do pass, I see that they're wearing headphones...
But I'm torn, because I think music would perk me up on a long ride, too. However, I think the bottom line is that even though I think it would be satisfying to combine the pleasure of riding with the pleasure of listening to music, I rely on my ears to tell me what dangers are around me, like it or not. And if I weigh riding with no tunes against being hit by a car or God forbid injuring someone else, no tunes wins.
I have been considering the boom box in the basket method, though. In the right environment, I think it could work.