I was thinking of stuff to use under the hood to clean off the gunk & protect what paint there is under there, and I saw my can of tire foam on the shelf!
I just foamed it onto the painted areas, let it sit a couple, and then wipe off the dirt & shine it up a little. Got some on the wires & hoses, but it should do them a little good too, because it's supposed to (moisturize?), clean and protect rubber stuff by design.
After treatment, I let it dry up a while to eliminate fire hazard.