Just as with coins, I think the patina adds to their appeal. I would neither clean them further nor re-paint etc.
I have no idea what makes one old decoy worth $100 (about the minimum here-abouts) and another worth nearly $1M. Certainly the maker, age, rarity, subject, quality and state of preservation are important. There are decoy shows just like there are coin shows but I have never been to one. I just may attend one and maybe learn something.
If you have a way to display them, I think that is what I would do. A handmade decoy is more interesting to me than a machine made oyster can - which many of my friends collect and display.
Thanks for posting them!