I got a rear view mirror for my bike helmet. Now I can't believe how long I have gone without eyes in the back of my head. I wish I could wear it all the time - walking around, at my desk, on the sofa at home.
The benefit is only partly about seeing dangerous traffic, though obviously that is upside. But that's like saying that the benefit of ordinary vision is being able to run away from predators. I mean, yes. Running away from predators and not being hit by a car are good things. But that's not saying much for the value of vision. The value is in the joy and pleasure you get from the entire visible world, including things like sunsets.
My rear view helmet mirror is like gaining a new sense. I am like a person born in 2D, on a flat piece of paper, suddenly perceiving depth.
I wonder about use cases for things like Google Glass. Could it be running metrics on the world around you? You'd be seeing graphs of things that you don't currently have senses for. Sub-scent chemicals in the breeze, like bionic smell. The temperature and humidity over the course of the day. Stray electromagnetic energy when a train goes by underground. A geiger counter. Ultraviolet and infrared vision.
Don't build a TV app for your omnipresent head mounted display. Create sensory apps and let their uses speak for themselves.