For the spit you could try using a clay bar. However if the previous owner has some acidic spit, it could of etched away at the clear coat which would require much more. For the plastics you can use a heat gun (keep it moving) to get the wax to pull back up and restore a like new look. You can probably find a video on youtube for the heatgun method. You can also use black leather shoe dye, it takes a few coats and you want to do 50-50 overlaps to keep it from streaking. Or some people use tire shine. Although oils from the tire shine just doesn't make sense to me because it'll intensify UV lighting which will make it fade even more over time. Or of course paint it black. The previous owner used a gloss black paint on mine and I think it looks outstanding.