I believe it also depends upon exactly what kind of edged weapon we are discussing. You mention Japanese weapons for instance which are always best presented in full polish. I believe that to a certain extent this is also true of Indonesian keris. It is a living blade culture (keris are still traditional worn in particular ceremonial situations). Tarnished silver and brass fittings and chewed up wooden sheaths could be seen as a disrespect to the blade.
This is probably less true of Civil and Revolutionary War swords.
So i don't think there is one pat answer that applies to all edged weapons collection.