As a former chemist/material scientist, I have done a lot of work with metals and electricity. From whatever has not been forgotten by me, I can say that polishing metals does change a component's electrical properties. This is easily seen via resistivity/conductivity. We often burnished our contacts(a pencil eraser or fiberglass brush can work well), and the differences were certainly measurable.
The way two materials mate together is a very esoteric thing. The overriding goal is to achieve what is referred to as an "ohmic contact". That is techobabble for saying that the two materials marry well. No two disimilar materials ever marry as well as the same material to itself.
Silver was always far better in making connections than gold, and silver alloys(platinum/silver or palladium/silver) were better than silver as time goes by. In fact, 45% silver/55% palladium has been used for about 80 years when it comes to REALLY critical connections(military, not audio). This alloy is able to very nearly achieve a TCR(temperature coefficient of resistance) of zero. Which means that when put through mil - spec testing, in this case measuring resistance over a range of -55C to +125C, the resistance almost does not change. And, that holds true over time/use/fatigue.
As far as how all of my useless experience translates to audio, that is a bit more complicated.
I will say that AudioQuest sure markets the importance of the surface quality of a conductor. But, I feel that the sonics of their cables are no more or less superior to anyone elses. They have always maintained that the music rides along a wire's surface, hence its importance. Theoretically, if that is true, doing away with the impurities(such as oxides and sulfides) on a wires surface would pay real dividends.
However, many a cable manufacturer asserts that what their cable offers is the key to good sound. Whatever that technology may be. Also, if Nordost's technique is being held up as the only way to produce a good sounding cable, then I certainly cannot buy into any of this argument.
While copper and silver do combine well(check out a phase diagram), the real reason copper wire is plated with silver is to make it last longer; economics. The long term effects of silver(or any material) coming in contact with another material is in question.
For example, current flow will cause silver to strongly migrate through soda lime glass. Think this is not a real world example? Well, many high end resistors(Vishay, Holco, etc.) are cermet(ceramic - metallic) in composition, using glass as their bonding mechanism. That glass can be made of anything, as electronic glasses are infinite in number. Hopefully, it isn't soda lime glass, but as it is dirt cheap, it is prevalent. The industry can show SEM(scanning electron micrograph) after SEM of silver migration through a conductor/resistor it is joined to.
From an audio perspective, I have heard Ray Kimber worry about the long term effects of silver plated copper. It was a degradation question, from what I remember. Both he and AudioQuest have always disparaged silver plated copper as sounding horrible; bright, irritating, splashy. Although, now I think AQ is selling a silver plated conductor. I guess whatever sells...
Personally, I believe that better sound can sometimes come about by using the same material from a cable's stem to stern. I have heard cables with silver plugs, solder, and wire, and the sound was quite special. Natural, smooth, grainless. Not that this is a do or die statement. There is no such thing in audio, or wire. And, I think, that is my real overall point.