But you're only driving one at a time-- I know you know the lighting is better on the newer cars but that doesn't necessarily follow that you MUST upgrade the Pilot's headlamps. I'd put in the
X-Treme Vision and also spring for a set of snow tires. Snow tires may have a much higher return on their investment than new lamp assemblies-- and at night on snow/ice you're going to be driving more slowly and more cautiously-- just be aware of your distance seeing limitations and the limitations of the vehicle itself. Unfortunately, there are no factory HID headlamps for that vehicle.
You can always reduce the insurance coverage for the bare minimum to be legal, and just drive it around a few miles every month to get the engine warmed up and any moisture in the oil boiled out, as well as redistributing the oil/grease in the differential(s). Just upgrade the insurance before the big trips so you don't risk your life savings (and home!) should you be found at-fault in an accident (or you could get an umbrella policy). (But now we're exceeding the scope of this forum.)
It does sound like you should really evaluate if you need this fourth vehicle. Maybe you can do an incremental upgrade to a slightly newer Pilot or similar vehicle. But one thing is that if you keep this one, you're ready for the weather event that you don't want to drive your new cars in if you can't help it. As far as rentals-- renting a vehicle is something of a pain (at least for me).
Majestic Honda sells headlamp assemblies for $189.88ea, so new headlamps aren't as far out of your reach as you might think.