To remove paint from Plastic i've always used Car brake fluid but left it applied to the plastic as little time as possible, i used to do this a lot when i used to be into model Railways & used to modify the shop bought railway engine plastic bodies with more detail to scale detail drawings of the real thing before re-spray.
As for paint on rubber has anyone ever tried brake fluid for this, i ask as i'm trying to remove black spray from the top of some Bass unit baskets, the paint has gone onto the rubber surround aswell! it's only a thin matt black by the looks of it & probably would come off with some 'T' cut or summert simular! it's not all over the rubber just around the edge that fixed to the basket frame.