So I took the year 1903 apart and pulled out just the Whistler material (1903 was the year Whistler died and the issues were packed with articles and appreciations, not to mention high quality plates). Though it didn’t sell as a low priced book -- as a breaker the value went up substantially. Just the six pieces about Whistler realized $175. The parts really are sometimes worth more than the whole.
I’m not the only one to tell you that the market is moving toward ephemera, and lots of ephemera is composed of the interesting bits of pictures and pages that come out of breakers. They are the canapés of print: small, delicious, uncommon and often sought after. While there may be dozens of copies of books around, frequently there are few or no copies of desirable ephemera cataloged (even though it comes out of those same books).
National Geographic magazines from the 1930s are an example of how something quite common sometimes sells better in parts than as a whole. I’ve been surprised how well certain subjects from this period do. Not individual issues, just the disbound pages with the article(s) or ad(s) of particular interest.
For example, the article on the Nomads of Central Asia published in 1936 recounts an arduous overland journey and has wonderful color plates by Jacovleff. I sold it not long ago for over $60. Not every NG is valuable or contains potentially valuable material. Some of it is pure drek and conversely, certainly some of the early ones are not breakers.
But if you've got a stack of NGs, especially from the 1930s, when circulation dipped, you could do worse than to carefully take them apart, throw away the junk and put respectable prices on the truly interesting, hard-to-find, or scientifically or technologically valuable ones. These include early aviation, early exploration of the Poles, travels by auto through remote areas; early undersea research.... the list goes on and on.
One book I found particularly useful in getting a handle on NG and its contents is THE NATIONAL GEOGRAPHIC SOCIETY 100 Years of Adventure and Discovery by C.D.B. Bryan, Abrams 1987-1988. This is a big book, packed with information and particularly strong on the early years. There are hundreds of copies available on line. The cheapest ones go for a buck. Buy it, read it - it will help you make money on National Geographic by filling in the back-story and adding a lot of the details that will help to make your descriptions more accurate and readable.
It also has a much about photography, photographers, film (including the coming of Kodachrome and the liberating influence of color and the 35 mm camera). I found the sections on aviation, undersea exploration and the early years of the magazine and its staff particularly helpful.