If you believe that oxidation is an internal process I suggest that you test your belief. Take a piece of oxidized silver and cut it open. Examine the exposed area and the inside area that has not previously been exposed to the atmosphere.
Silver will not tarnish if it is coated. Tarnish is caused by oxidation, the process of the metal interacting with the oxygen in the atmosphere. If there is a protective barrier, oxidation will not occur. Protective barriers will need to be reapplied because they will wear off over time.
Of course excessive polishing will wear down the metal. Polishing is an abrasive process.
You are correct that Argentium Silver does not contain nickel, but neither does traditional Sterling Silver. Traditional Sterling Silver is an alloy of 92.5% Fine Silver and 7.5% Copper (which is why Sterling Silver is stamped .925). Argentium Silver is a type of Sterling Silver (it holds the same fine silver to non-precious metal ratio), but it is alloyed with Germanium instead of Copper.
I have worked with numerous alloys, including Argentium Silver. The cost is not what concerns me, several of its working properties are undesirable. It is better suited to some applications, but certainly not others. I would be careful about making a blanket recommendation concerning this (or any other) alloy.
** former username Ealaiontor **
"The truth is I've never fooled anyone. I've let people fool themselves. They didn't bother to find out who and what I was. Instead they would invent a character for me. I wouldn't argue with them." - Marilyn Monroe