At What Grade Is Value Unaffected By A Coin Being "Cleaned"?

Logically, this should indeed be true and logically, I agree with you - every coin should have "bullion value" and "numismatic premium" components of its total value and these two halves of the total value should go up and down independent from each other, with the respective markets in question. The demonstrable fact is, that they do not. The reason behind this is to be found in in human nature rather than in as a property of the coins themselves, because humans as a whole are (a) illogical, and (b) lazy.

Coin collectors simply don't want to pay extra for their coins, just because some silver pundits trading paper-silver reckon they theoretically should. So in a precious metal price spike, the total price of collector coins does not rise anywhere near as rapidly as the silver price does. So, in effect, when the price of bullion goes up, the numismatic premiums on collectable coins go down - because there are fewer and fewer collectors to be found willing to pay that premium, on top of the increasing silver price. And so, as numismatic premiums shrink to zero, more and more once-collectable coins get tossed into the scrap heap - literally, sometimes.

Fortunately, most dealers won't instantly dump something into the junk bin just because of a spike in precious metals. PL/MS 10 and 25 cents from the early 60s are next to impossible to sell at much of a premium. That being said, I've hoarded a fair bit, when in the future, it will be worth more than the melt value. Of course, I'm sure every other dealer does the same thing. We're all waiting for the numismatic value to go up, but none of us want to blink and melt the stuff to make that happen!