I can appreciate your confusion Sharkman. One wants to purchase coins that they themselves appreciate, as well as others, because you may want to sell one day.
I think there is clearly a balance here. No one wants a bright white dipped coin if it is obviously worn at all (AU and under grade) because that looks wholly
unoriginal. But overly dark toning loses eye appeal even on higher grade examples.
Personally, I don't like the reverse on CaptainFwiffo's 44-S
Mercury dime. Obverse looks phenomenal, but I find the toning on the reverse to be so extreme as to obscure the surface features.
I've been considering this 28-D, which looks to be in AU grade but has some pretty significant toning on the obverse. Any lower grade on this and I know the toning would bother me, but on this AU it seems ok and with so many over dipped coins on the market, this is nice to see.


Based on the link that John1 provided (thanks!), PCGS would likely say this obverse has below average to negative eye appeal. [
https://www.PCGS.com/eyeappeal]
However, I see hints of circulation cameo (llewellin had a comment about this effect) and at this grade it just looks so much more "original" than much of what is out there for sale. I like "crusty" coins like this because this just speaks to vintage-ness or antique-ness.
Regarding the
Trade dollar thread. I agree with some others that is is somewhat hard to compare as Liberty's head has so much more wear on the toned coin than on the un-toned coin. I think grade should be the primary consideration, then once you've settled on the grade you are looking for, toning/"original skin" is the secondary consideration.