I painted all my black plastics in March of last year... 6,000 miles later, they still look brand-new.
I washed everything with dish detergent, and painted it all with Krylon Fusion (about two coats). People still come up to me asking if it's a new bike!
I've heard great things about SEM's vinyl dye; it should work better than Krylon.
I painted my old Elite 150 (the entire body) in red Krylon Fusion, with a clear top-coat; came out looking like a million bucks, save for the orange peel effect...