These are great observations. Indeed I've come to a similar conclusion in the past. Now when I walk to class, I like to take the wooded paths, look around and observe nature, listen to the birds and the rustling of leaves and squirrels in action (though I do find those blasted animals annoying), and marvel at the sky.
However, the "not-listening to music to take in and appreciate the world" concept/goal does not really apply to those who live in factory and mall-laden cities. When this has been my case, I put on my headphones without hesitation and use my time to listen to a piece. Hell, often times I'll forget where I'm going, or I'll miss a stop or a turn, but that was because I was paying more attention to the music to begin with. I don't see why it should be otherwise, since in this scenario you are using your time to the fullest as opposed to making your way from one point to another through a heap of soulless bodies, obnoxious smoke, and annoying tire-screeching and honking.