From my experience, there's definitely a premium with all the blue background cards in general. I'd say 2x the value of pastels at least...for some of the top-tier HOFers, maybe more. The blue backs are extremely attractive cards, like Leon was saying, although I'd say they're more plentiful than the "Over 300 Subjects" backs.
I think the Sporting Life agreed on the "eye-appeal" factor as well. In the rare instances I've seen ad-pieces or panels from this set, they've always consisted of bluebackground cards like the group below....
m116ads.jpg