I have a friend with an almost complete set that every now & then offers, (or threatens), to give to me. Do I really want a yellow elephant? Not because I think they are worth anything but I value the historical viewpoints of any old book or magazine.
I have the Nat. Geo. set on CD - very poor quality scans of the images, have heard the DVD reissue is somewhat better, but still not the quality of the dead tree version.
Now I'd love to have a complete collection of Popular Mechanics, Mechanics Illustrated or Popular Science, but I'm not going to pay ten or a hundred dollars an issue, which is what the Internet sellers want, (they may sit on that magazine for ten years or more before they find a buyer), but I might pony up a few dollars for a well scanned set if the publishers were to put one on the market.
I believe that the entire Popular Mechanics archive is available on the web.
The few scans I have seen looked very good. Here is a few quick Google search links on the issue
http://www.popularmechanics.com/technology/gadgets
http://books.google.com/books/about/Popular_Mechanics.html?id=Vc8DAAAAMBAJ/news/4295218
Regards
alfa6 ;>}