As a long-time viewer of Antiques Roadshow and an omniverous reader of all things guns and ammo, I would say, as a general rule:
If it was made to be collectable, it isn't.
This is equally true of Hummel figurines and Winchester commemorative 94's. Forget Franklin Mint.
That said, in firearms, markings on the gun are more important than a medallion in the stock. Receiver crests seem to command a premium, from an intact chrysanthemum on an Arisaka to an American eagle on a Luger. Mauser 98 collections are built on national crests.