Sight seems to be a sensation that is decreasing in acuity. At least, it has more competition from in cockpit PDAs, electronic varios, electronic maps, and FLARM displays. I have shared thermals with pilots who have made more than one circle with their eyes and fingers down on the panel, NOT outside the cockpit. I have had several close encounters with other gliders where the pilots face and eyes are involved with the electronics, NOT outside. I had a pilot who was new to the area tell me with great enthusiasm how he had programmed his two handheld Garmin GPS units to use while flying for his gold badge and use that information along with several pages of finely printed numbers to help him make go/no-go decisions. I flew beside him on the same ridge for several miles and he never looked outside his cockpit once.
We do need passive systems that are always on.