I purchased the book because I elected not to book a tour. I finished roughly half of the book on the train to Machu Picchu from Cusco through the Urubamba valley. I found the author's enthusiasm contagious -- by the time I arrived in Aguas Caliente, a short bus drive away from the citadel, I was excited. It was only after I physically ran into the entrance to the trail leading up to Huayna Picchu at the northern end of Machu Picchu that I learned the trail was open to the public to hike.
Huayna Picchu is the imposing peak that appears in the background of the most common image of Machu Picchu. Its peak hosts architectural structures of its own, and provides a spectacular aerial view to Machu Picchu. The very steep trail takes about an hour to climb. It is a site not to be missed in my opinion, but one has to plan in advance to visit, primarily because the entrance to the trail closes at 1pm. Huayna Picchu, though its name is mentioned in the book's preface, is not dealt in detail until close to the end of the book. This is why I suggest readers to at least skim till the end of the book before arrival.
Other reasons why the book should be read prior to arrival are for the obscure artifacts. For instance the image stones on the walls of Intiwatana (the principal temple), which supposedly represent (and replicate) the surrounding mountains can easily go neglected if one hadn't read the corresponding entries in the book -- the stones look like natural stones placed where they are by happenstance unless one knows of their significance a-priori.
The book is thorough, serves its purpose well, and as pointed out earlier, does not fail to convey the enthusiasm of the author. However I think it could have made better if it included a list of locations not to be missed upfront. Hiring a local tour guide arguably is the best option, but the book is the next best thing, especially if compared to other self-guides in print.