Yeah, I always valued the scans here of stuff that's hard to find otherwise. I use this site to supplement my collection of back-issues and reprints. Scanning in the Showcase stories and spending all that time coloring them, when they're already out there for 9 bucks a volume (6 if you look in the right places!) seems a waste.
As far as getting out that yellow, I've had some luck with it in Photoshop. I start by using the "Adjustments...Levels" control to establish a ballpark black and white, then I use the "Adjustments...Selective Color" and select "Whites". From there, you can bleed out all the black, magenta, cyan, etc so the white is true white.
Before: 
After: 
It's amazing, really, that pages that seem to be still pretty crisp to the naked eye come out so muted and yellow when scanned.
And I kind of like the dots, sometimes.
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