Great post. We always slow down to visual range when the fog, darkness, rain etc impairs visability. I have had radar on my boats for over 30 years, and lusted for it before then when it was not affordiable to us. It is a great tool. BUT not all boats show up on radar--as mentioned--Kayaks, some glass boats, small boats, debris, dead heads etc. So radar is never a substitute for eyes. I have not yet sucumbed to an auto pilot on these small boats. Part of this is my adversion to running at a high speed on auto pilot. I think it is dangerous for many reasons. Just my opinion and I have had auto pilots on my boats since 1962. Great tool!
We have one person assigned to the radar/chart plotter. The skipper has eyes on the water; even with low visability. Even at 6 knots and 100 foot visability, the reaction time of going from an observer saying "I think I see something at 10 o'clock" to "Where?" to "There", is too long, and you might run down an object/boat. Thus we feel that the person at the helm in one of these small boats needs to be eyes on the water in very bad visability.
Take, and again, Thanks!