My observation is that - if you've got a truly collectable ANYTHING the original finish commands a higher price than a repainted one.

Furniture, guns, bikes - same same. Collectors want original above all else. Only if the item is a total wreck and devoid of a substantial amount of its' collectable value should you consider repainting. With an eye towards preserving the collectible value of any item, careful cleaning and preservation should be your top priority. And with some items cleaning removes patina, which is also highly prized in some circles.

John D.