yeah on swords I have never heard of a collector who said "leave that rust on the steel" and the petina remains even if you polish it out , because age goes into deep surface loss already , hence cleaning old blades is something lots of people do ,this is probably only true of weapons. I mean on a gun I can run steel wool over it and oil the furniture and polish the steel, as long as I dont grind away the metal it does not affect the value on bit, in fact a brand new looking old gun sells a lot better than a gun with filth all over it , same with swords and all weapons in general, if there are two minds on the subject I am def with the camp that says "treat them as they should be treated" like weapons.
the only thing I would not say restore is truly ancient weapons that are almost all corrosion or ancient bronzes
otherwise active rust should always be neutralized and oil and or wax should be applied to preserve the state of the steel as close to original as possible, also in some weapons the surface filth hides the truly interesting pamor , and im all for polishing that out so you can see the lines better, never seen a blade lose value due to that either( mind you this is on things prob in the last 200 years , I can see 500 year old blades being polished at all and losing value, because they have almost none of the original material ( save in very rare cases) surface wise I mean, well its all original, but even if polished would still look really corroded adn you will just lose the bits of metal sticking out , but i dont own anything that old so thats all conjecture , huzzah, but my naga dao, kachin etc all that stuff, I have treated them like HI blades( oil and clean and hang on a wall, but kept as if they are going to be used even if I never will