I've done several using Dupont vinyl paint. It's mixed using vinyl resin instead of balancer and binder. The vinyl resin comes in low, medium, or high gloss. My Dupont book says to use high gloss on vinyl tops but it's a little too glossy for my taste. Medium isn't quite glossy enough, so the next time I have some mixed for a top I plan to have them go half medium and half high gloss with the vinyl resin.
I, too, use whitewall cleaner to clean before paint. Scrub well with a brush, rinse thoroughly with clean water, and let dry thoroughly before masking and painting.
Going from black to white will probably take 1 1/2 quarts. Just a respray in the original color to freshen up a top will take a quart. It will probably cost around $80 for 1 1/2 quarts. Properly prepped and maintained it will look good for a long time.
Dallas