This is a fun post to read through. We have recently had this discussion amongst me and my canyoneering friends. It was a mixed bag of not sure. We have never hiked with music before. I like listening to my headphones while running and doing yard work as well as out on the boat on the lake, why not hiking. On some of the search and rescue calls that I have been on some of the guys wear their headphones on the hike in to the patient (they took them off when the real work started).
We tried it one day with a canyon, just on the hike in. We packed my iPod and a Goal Zero Rockout Speaker and played it on the hike in. This day it actually became a nuisance for me to have it, but it was more because we took some of our kids through the canyon with us and some of the songs were not kid appropriate so I kept having to fiddle with it to skip songs. Generally I have always hiked without the music, but I am not opposed to putting headphones on next time and trying it out again.