I've enjoyed great resuts with DursGloss 481 Wax eraser & DuraGloss 271 Rubber Bumper & Flat Black dressing.
My application was to get splatter from paint cleaner off the black plastic cowl under the wiper blades. The DG 481 removed (not hid) all of the splatter with 2 applications. If you like apricots you're in for a treat, as that's what it smells like. perhaps there is a citric type acid in there.
The DG 271 is awesome on black plastic and rubber. it's not like a dressing, but more like a polish. My black plastic and black rubber trim always look new with this, and it lasts for months wint NO running when it gets wet.
The Wax eraser states it's safe if it gets on paint. The Dressing would probably wipe off paint with a micro fiber towel if any were to get on it (a QD to might make it easier if it gets on the paint, but it's probably safe). You could also use blue tape around the edges of the spoiler to play it safe.
Best of Luck!