as a 'detail' guy, nothing more disappointing than black trim faded to light gray...
I recall reading about someone using Vaseline petroleum jelly on old, faded motorcycle switch housings. Slather it on and let it sit for a day or 2 before removing...some swear by using a heat gun, but many say that is only temporary.
Lots of expensive liquid and gel trim restorers on the market..you hear mixed results. One thing that is supposed to work well is ceramic coating. Griot's Garage and others sell ceramic trim restorer wipes.supposed to work very well.
Ultimately your paint idea may be the best. Using a plastic specific spray paint could be a great, inexpensive, long lasting alternative. With the light usage your scoot will get it may last forever!