I bought a factory manual for every car or bike I've ever owned, and always thought it was the best investment I could make. True, the Chilton's, etc. manuals are fine for finding out where the spark plugs are located, but when it comes down to really getting into your vehicle, then the factory manuals can't be beat.
Another problem with the Chiltons/Haynes manuals is that they try to save money by combining several years and models in the same book. Great to a point, but when you need real data, they're just frustratingly useless. For example, my new R1 came delivered to me with a loose steering nut. Looked in the Yamaha manual and found the correct torque to be 80 lbs. ft. Try finding that in your Chilton's!