Jack, I'll go along with what was said about "Actual Photographs " of some of the less common pumps , Keese, Clear Vision , Crouse , Springfield , St Louis , Brown, etc. Then too, I know Half tones increase the price of book threefold . I was in the graphic arts industry and yes, I have a working knowledge of what happens to a photo when it's made for publication .
Perhaps a couple of shots of some of the really rare or hardly ever seen dispensers might be in order . having it as a Hardback definitely increases the value , but , you have to convince a publisher it's worth the extra money to invest in it .
I never asked the publisher for a re run of a Political science book I did before I let Scott Anderson run off with a lot of material he used in his book, Check the Oil . At that time , the market was too scattered and I too was badgered as to "Values " for a re run . Since I refused , the two publishers simply told me , It wouldn't be a book they could invest in.
Ed Shaver