I say don't do it - unless you want a gun with that "restored" look. Ick.
There are very few people out there who can make an old gun look new or more appealing. Most of the time they just mess them up - ESPECIALLY the checkering. That's where 99% of them really blow things.
Personally, I think old guns should look old. I like the wear, the scratches, the dings. That's the gun's history. As long as the gun is mechanically sound and secure, I say leave it alone.
Just call it "patina" and people will pay you a lot of money for it.
If you want something nicer, sell the gun and buy a piece with more original condition.
I will not buy a refinished gun, so no, I don't think it increases the value.
OWD