One thing there is no shortage of, right now, is of drum stuff to work on. On this blog, we're barfing up mass quantities of new stuff on a quasi-daily basis— more like quasi-weekly, recently— and there are hundreds of books out there, and reams of new stuff in the drumming magazines every month. It can be overwhelming for students, who feel bad because they're not learning all of their books cover to cover, or because they haven't really “learned what they already have in front of them.” And writers like me can wonder just what the hell is the point of doing more. Hasn't everything been done already?
These feelings are wrong. I own over a hundred books, and may work out of out of 15-20 of them in the course of a week, and I still need to write more stuff.
Drum books are an incredible value. If you learn one thing of real value from it, what did it cost you? Around $8-25, usually. And by “learn”, I mean you acquired something in your playing, and maybe some verbal information about music, and/or gained some kind of general understanding that actually helps you in your playing. If you're able to dedicate dozens or hundreds of hours of practice to a single book, you've really gotten value much greater than the book's cover price.
Format and organization matter. Especially when you start using your materials creatively. Little changes in format, can make big differences in what you can easily do with the materials, how productively you are able to use them, and what you learn in using them.
Remember, it's a multi-year, multi-decade process. You're going to have these books around for the rest of your life. Maybe you'll find a use for some other parts of them in five years, ten years, or twenty years. Don't think of a new book as an assignment, think of it as an addition to your library; a resource that will be instantly available if, someday, you need it.
Limiting yourself to one book you are really limiting yourself to one author's vision, to the extent that he was able to put a complete vision accurately into book form. No one is able to cover everything, and not everyone is that good a writer; nor are everyone's methods are good enough to dedicate years of your life to working on. And just because of the nature of communication, you may need to hear the same message put several different ways to really understand it. So I'm extremely skeptical of very expensive all-in-one collections that claim to cover everything you'll ever need to know and practice.
The exception to that is the body of methods associated with Ted Reed's Syncopation— an $8 book. Most players could just learn that really well, listen a lot and play a lot, and be done with it. You can become a great drummer with just that, and you'd be missing very little of practical importance. Still, it doesn't cover absolutely everything.
You're supposed to have a lot of books. Especially if you're teaching. As a professional, you're supposed to build and maintain a personal library both of books and recorded music. It's just part of your infrastructure.
Just what is the point of writing more stuff is a larger subject I may have to save for another day. I think that if you're thinking about the playing process, and the practicing process, and writing for contemporary needs, there will always be room for more materials.