When to restore?

[Parkerman]

When, or maybe IF, to restore? If it is a limited mfg. gun, or rare (an off-beat gauge), or a one-of-a type of engraving, etc. --thing twice about "restoring" for in the process you will alter the gun so that it loses at least a part of its value. If the mechanicals are such that the gun can't be fired and you want to hunt with it, get it fixed(split barrels, rust, etc.)
If the gun is just a good shooter and that is what you want with no regard to appearance, leave it alone. However if you are concerned about the lack of great case colors get them redone and enjoy it further.
What is done to the value? To a hunter looking for something to shoot with, probably very little. If it is a rare gun, limited nos., etc. you will probably reduce the value considerably.

[Austin W Hogan]

I think the choice is relatively easy. If a Parker gun is beginning to show rust pits on barrel or frame, it is time to arrest the rusting process. A gun that is shiny, but not rusty , still has enough rust resistance to carry on even though the visible barriers ( blue, case color) are no longer there.

Best, Austin