0000 steel wool, your not gonna have the shine of new plastic, but it will take some off and brighten them back up.
you can also use mop & glow, this will put like a wax coating on them and give you a nice little shine. the finer stuff you use the better they will look. just dont go crazy and start sanding them with 80 grit. you can also wet sand them. just use very fine material. they will always be brittle tho if bike sat outside most of its life.

I've sanded down the surface using 600 grit wet & dry then washed the bejezus out of it... Then let the plastic sit out in the sun, ran hot water over the spray can & applied light coats. It's probably rebadged krylon clear but I had good results ymmv

that blade is a ton of work, easy to do on a dirt bike, way less fender to clean. use the steel wool and call me in the morning. lol

i have used what i said before, i also used plastic wax when i was done on a high speed buffer, when you start sanding
make sure to go the same way all the time, once you put the cross hatch marks in it they are a pain to get out.