Yes...this stuff works great on gas tanks, dash panels, etc. As mentioned earlier, Rust-Oleum makes a similar paint for plastic....which I'm sure works equally well.
As with any painting project, preparation is the key. Getting the surface absolutely CLEAN, and oil and grease free is the key.
These paints are available in satin black or gloss black.
I'm not sure how it would work on the rubber passenger side handles....
I hose those down with some white wall tire cleaner (sometimes several times) to melt away the oxidized, nasty brown rubber, and then give them a spray of "Armor-All" or something similar.
As most of the members on here would probably agree....you can't trust those 35+ year old handles to perform their original function....they have lost most of their original strength, and now perform mostly a "decorative" function.