Huh. I read some - far from all - of both Nancy Drew and Hardy Boys as a kid. But the editions that I read were newly-published ones. I don't remember any glaring racism in the books offhand (though it was a long time ago). I guess that is consistent with the bit in the book that you read, that mentioned that the books were revised.

Mostly my memories of the books are:

- I liked the Hardy Boys better than Nancy Drew because their adventures were a balance of physical and cerebral, rather than mostly cerebral, and because they frequently got themselves out of trouble rather than getting rescued by a man. Even at the time I interpreted this difference in the series as sexism on the part of the authors, but I knew they had first been written "a long time ago" so I shrugged it off.

- My favorite character in Nancy Drew was George, the athletic quasi-tomboy. In retrospect, I think it's interesting that Nancy's friends were a thin relatively-masculine girl and a fat feminine girl, and that it's sort of refreshing that whatever else was in the books, they were willing to have characters that didn't totally conform to female gender expression expectations or societal standards of beauty.