I believe that each gun needs to be looked at individually, when it comes to cleaning and restoration. Patina is a good thing, rust, corrosion and dry rot are not. My Henry Tope rifle, which can be viewed here in the Library, was found within the last ten years in the top of an old barn. It was so filthy that you could barely tell that it had a patchbox, nor could you begin to identify the wood. The barrel was covered with rust scale and the bore looked like the inside of a brick chimney. I could have left it just the way it was found. If I had, I would never have known that it was the only signed rifle by this maker that has ever turned up (and he worked about 30 miles from where I live) because the script signature was hidden beneath the rust and dirt. I would never have known that it was stocked in very nice tiger-striped maple, because the wood was totally black with soot. I would never have known that the bore was actually quite good, because the farm dirt that was stuck to the old grease that had been placed there well over 100 years ago, would still just look like rust. I'm not saying that careful cleaning is always the right thing to do, but in this case it certainly was.
On the other hand, I have a grand old Plains rifle, by J J Freitas, Springfield, Illinois, that turned up in California. It shows lots of use, but not abuse, has a makeshift repair, no doubt done around a campfire, and looks as though no one has touched it since a buffalo hunt in 1880. It is one of those guns that makes you say "If only it could talk!" I would not clean or restore this rifle in any way, under any circumstances.