Well, I have heard that bullion collectors love 'bast white' and such, so if you want to go this route, it's all up to you. I, on the other hand, wouldn't apply anything stronger than pure acetone to any of my silver objects.
I'm not above a dip every now and then, and don't find too much wrong about the washing soda/Aluminum treatment. It all depends on how you prepare the surface and how you clean and protect it after treatment. (IMHO)
I've used it on silver plate items for years but the tarnishing always comes back no matter how well I keep anything stored, therefore repeat and rinse, repeat and rinse. Eventually the silver plate will wear doing this over and over again. I'm not going to try it on my bullion. But these are yours and of course you can do anything that you want, won't take that away from you or criticize you for it. If (my) bullion tarnishes I'll leave it alone. For me it is just bullion.
Actually I just won a 1/2 oz proof Libertad that looks milky in the pictures and I fully intend to dip it. I'll try and document it.
I'm no expert, and don't know what long-term harm, if any, it would cause, but for bullion bars as you've shown why not? They do look shiny after. And they are yours so you can do whatever you want. I obviously wouldn't advise using on any numismatic, or even collectable bullion due to the hairline scratches from the cloth, or whatever you use.
I've dipped a few using eZest. Even taken a Q-tip to a couple stubborn tarnished spots. Others I leave be.
I am trying to figure out, why there would have to be any long term damage ? Or what that would even be ? all I can say it does a great job, from the example I posted, also will be using it on a couple other non pre packaged bars that I have Also FYI, I did take a high power loop and examined the bar with no such scratches Observed, again we are only taking about a small amount of cream on a polishing cloth and just a couple of passes, and for the paranoid...LOL, would probably not Use this product on anything they would be overly concerned with.
It does take awhile for tarnish and toning to show up, but it also depends on The climate you live in, I live in Las Vegas so it is very dry, so maybe polish Once a year if that, to keep things looking good I do agree with most of what you said however I did sell a $100 4oz Silver Plate, that I could of got over spot for if I would have new in advance before I sold it and the tarnish removed ( basically could have resold it, in the store) But because of the tarnish it was sent strait to the refiners.
No scratches from the cloth, scratches from the abrasive in the cleaner (silica) or from grit on the object being pushed around by the cloth.
The thought is that if you leave any of the cleaning material on the object, time will allow it to react with the object.
You say it's the compounds/cleaning products that cause the scratches, but I'm pretty sure that rubbing silver, as well as other metals, with any cloth can, and does produce hairline scratches. Please correct me if wrong. Using the cloth with no compounds would leave hairlines is my understanding.