I just received volume 4 of Christopher Alexander's "The Nature of Order". I am not going to read it until I have also received the third volume. I am waiting for the day when all four volumes have been received, and I can read the volumes one after another.
According to the author, the four volumes were the result of 27 years of effort. Of course, he did not spend all his time on the books in those 27 years. However, I do understand how writing a book can consume an author.
He is not the only one spending decades writing books. Donald Knuth started his "The Art of Computing Programming" in early seventies. He quickly published the first three volumes, out of possible seven volumes; spent a decade on computer typography; and his fourth volume has been annouced for more than a decade now, I don't even remember. When his volumes are done or when he dies, whichever comes first, I will buy the whole set of that set of books. Right now, I already have most of his books.
So, is it worth spending decades on writing a set of books? I don't know. I am not good enough to have enough materials to writing a whole set of books. I might be able to get away writing one book here and one book there; I will never be able to writing a multi-volume book in one area.
My dream is to be able to spend a few months writing the book I have in mind for more than a year now. This will remain a dream until who knows when.