I think it is important to find the publishers and authors who are considered the authority in each field.
For instance, I've seen a million toy train books. There are tons of books about toy trains with color pictures, most often printed with outlandish prices, but Greenberg's books on Lionel, Marx and American Flyer are the gold standard within the hobby.
Never in my life have I heard anyone at a train show say "What's the Kovel price on that?" At a train show, the 'book price' that everyone refers to is Greenberg's.
In the stamp collecting field, Scott's is the authority.
Like Dig said, figure out what area you want to study, and find the authority publisher in that field.
And, before you waste a ton of cash on books, check out your local library. Even our local two horse, Podunk town library has a boat load of collector books.