In fact, he was so prolific and well-known that later in his life, some hobbyists actually started complaining about seeing his stuff so often in the pages of Model Railroader magazine and elsewhere, but really... he was the one that blazed the trail for high quality photos of model railroads, and he remained on the cutting edge of the hobby until his untimely death in 1973 of heart failure (he was diagnosed with a weak heart early in life, and in every picture of him I've ever seen, he appeared plenty pudgy---back then the relationship between a healthier, slimmer lifestyle and heart healthiness wasn't really something that people thought much of.)
His railroad, which was (and probably remains to this day) the most well-known and respected model railroad ever built, sadly was destroyed in a housefire less than two weeks after his death, but his legacy remains with us today. Check out, for example, this link, which attempts to document online what we can of the railroad.
Before the age of the internet, though, Allen's longtime friend and former Model Railroader editor Linn Westcott gathered everything he could on the railroad and wrote the (at the time) phenomenally thick (and expensive) paperback Model Railroading with John Allen which is chock full of color photos, mostly taken by Allen himself, as well as an in depth description of the railroad, John himself, the operation of the G&D, and John's own lead-up to the G&D super project via his earlier incarnations of the railroad. In a twist of irony, Westcott himself passed away after preparing the manuscript but before it went to print.
In my teenage years, when the model railroading bug first bit me, I bought a copy of this book (which is now out of print and sells at a significant premium online) even though it was more than twice as expensive as any other book by Kalmbach on model railroading (ah, the irony. Prices of all the other books have caught up to it such that the price I paid for my John Allen book would be middle of the pack now. Keep in mind, there has been at least one paper pricing crisis that really hurt all publishing industries, and caused massive increases in book prices since then.) Although the binding on my copy isn't the best anymore, otherwise the book is in great shape, and it's tons of fun to browse through it to see what all the fuss about John Allen was about during the 50s, 60s and into the 70s. He was one, talented guy.