The difference (in my mind, and with my 40-something eyes) is that it's
harder to see stuff in the cockpit at night. Every task from instrument
scan, to reading a chart, to tuning a radio, to copying an in-flight
reroute becomes more difficult.

My eyes are not quite 40, but I have much the same problem in most
airplanes. However, most GA airplanes do not have anything resembling
an adequate lighting system.

Clue time - if you need a flashlight to perform ANY task in the
cockpit, your lighting is inadequate. A flashlight is an emergency
backup, not for normal inflight use.

I don't worry about single pilot night IFR in my airplane, because it
has an adequate lighting system. Someone, somewhere along the way, did
most of what was required and I filled in the rest. That includes
pilot and copilot overhead map lights with yoke-mounted actuation
switches - so you can keep flying the plane while reading the map. It
also includes panel lighting for all the instruments and overhead
lights forward and aft - each with independent switches. The only time
I use a flashlight in the plane is for startup, so as not to run down
the battery.

Once adequate lighting is in place, there's really no issue. However,
as I mentioned before, most GA airplanes do not have adequate lighting.
I've never seen a rental that did. On the other hand, I think you're
pretty much taking your life in your hands flying a rental night-IMC
anyway.

Michael