Thanks, folks - it is appreciated
Full credit to WWDiesel as well - having him also dealing with the problem has been invaluable.
Today's stuff (which actually started on Thursday): hit the front wiper arms and plastic end supports on the roof rails with
Rustoleum Truck Bed Coating. Preparation consisted of nothing more than removing the pieces, washing them in dish soap (Dawn, for anyone who may be wondering), giving them a good rinse, and then letting them sun-dry before hitting them with the bed liner spray.
No pictures because, frankly, my camera can't show the aftereffects well enough, but I'm pretty happy with how they came out. The Rustoleum bed liner spray has a rather fine grit to it, much less than something like a Line-X or Rhinoliner. It sprays like a slightly thicker paint, which it essentially is, and once dry feels very tactile without being grating.
These were my guinea pigs to see how the spray behaved on both plastic and metal with minimal prep; I've worked with heavy-duty spray-on bedliners before, but never something like this. For the price ($8/can at Home Depot), it's worth it if you're also looking for something to restore fading plastics and paint with as I was. Time will tell how it holds up, but given that I never want to have to redo this on the things it's intended to be used on, I'm optimistic that it will last.