I've worn an iPod around. We've had some good times. But I'm not sure headphones in public are a good idea. There are reasons to listen to the city: opportunity, absurdity, danger. There are musicians and crazy people that you need to hear.
If you wanted to mask one of the senses, it would make more sense to stick tubes in your nostrils, and have recreations of scents piped in. You'd be more present and aware, and still get to customize a piece of your relationship with the sensual world. You think walking around listening to senior year's cruising anthem is evocative, imagine the possibilities of a scent playlist on shuffle:
2 minutes of Wisconsin Prairie, 2:40 of lilac, 4:45 of barbeque, 1:07 of fresh donuts, 5:00 of the aroused genitalia of a fondly remembered lover, 2:10 of coffee brewing, 6:20 of cookies baking, 3:53 of popcorn, :30 of hot car, 3:00 of sunscreen, 1:00 of White-Out, :45 of Aqua-Net.
The technology is almost here. Walking around with wires coming out of your nose is no more ridiculous than having wires coming out of your ears. And you'll hear the horns and old acquaintances that are calling you.