I bought this book years ago and refer to it often. Our first Disney trip I was clueless as to where to begin planning, and this was my go-to each time I had a question. It saved us over $1000 the first trip. In my opinion it's worth it, but that's also how I found this website.
Alot of people will say it's not worth it, since you already know about this website and get alot of great advice here. But I have personally always thought it was the best $15 I've ever spent! We have been to Disney several times since my purchase, because I could do it affordably for my family, from ideas in that book.