I've been using a reproduction 37-39 standard (not the deluxe) Ford wheel for a while, with about a thousand miles now on it. I never painted it and the rim has gone from a flat-black to a semi-gloss. While the spokes have remained flat due to the fact I don't hold the wheel by the spokes.
Because my car is black inside & out, I'm considering polishing the rest of the plastic wheel rather then painting it gloss black.
Generally wheels were painted, out of the factory, to match the interior.