Not necessarily. I’ve seen raw $10 and $20 gold pieces in attractive EF condition for slightly under the spot price. The St. Gaudens $20 might be different. These were Liberty pieces. I have also seen modern commemorative gold coins offered for a tiny percentage over the spot price. These coins were available in quantity.
Isn't the problem with many "blast whites" the possibility/probability that they've been cleaned or dipped ?
As a GENERAL rule, the AU-58 advantage might be true. But I'm sure there are some 62's that can compete on eye appeal. It's probably a bigger advantage when comparing MS-61's and 60's. You don't even see that many MS-61's/60's up for auction or in dealers cases except for rarer coins. Not many people are going to buy an MS-61/60 Saint or Morgan unless they get a good deal and they're buying bullion or quasi-bullion.
I have a few of those acquired over the years in TPG "slabs" with "rub/bag-marks/scratches/etc.", but regardless, the plastic improves re-sale! JMHO