It all depends as to whether there is adequate collector demand. No matter what the item (guns or anything else), there will always be some which have no, or very little, collector demand even in brand new condition. Think of a pot metal Saturday Night Special. Case in point - last weekend I ran across a guy who wanted to sell or trade a Hi-Point .45 pistol, wanted $350 for it because he thought it was "collectible". Even for someone who wanted it, you could probably go out and buy a new one for $150 or less. And it is in no way collectible, and probably never will be. Another consideration is that what is in high collector demand today may not be tomorrow. And vice-versa. I imagine that 50 or so years ago, a Registered Magnum sold for little to no premium over any other N-frame in similar condition. It was just another gun.
Otherwise, it comes down to scarcity and condition, and possibly other factors such as a specific association with some famous or notorious person and/or historical event (like John Wilkes Booth's Deringer or Jack Ruby's Colt Cobra).