It is often said that we're only using 10% of our brain or so. Might be true. But of course in general we're only using 10% of our body as anybody can attest who has been doing a stiff workout program without preparation - all those unused muzzles complaining suddenly. And all those nerve cells that we could use to feel pain, heat and pressure - usually they are just asleep. But we could use them to extend our capabilities.
A couple of years ago there was an experiment where blind people were given back a limited sight ability by hooking up a camera to a device on the skin of their back that would exert pressure according to what the camera saw. I can't find back the link, but I think the resolution was rather limited, so there might have been only 80 pixels in a row or so, only reacting to light and dark. Still it had some value. This is a typical example of using those nerve cells that are doing nothing normally. The amazing thing of course is that the brain figures out pretty quickly what this extra input is and what it should do with it.
Most people can already see, however, so for them it is not very useful. However, I suspect we can create a very similar thing to make ordinary people see in infrared/ultraviolet or maybe sonar or radar. And while were at it, adding a little compass to shoes could make your feed aware of what is North. I trust the brain will start picking up these signals and give the direction sense impaired a better change to not get lost.