I do it if it's something that is in enclosed area and generally doesn't get much contact with fingers, etc., otherwise as
@seber stated, I don't find they last very long if anything rubs against it.
I've tried lightly sanding prior to application, etc., but I suspect many of the plastics are just not conducive to paint adhesion - at least with the solvents in ubiquitous paint pens, etc.
I've never tried any paint with an etching solvent though.