Everything in 9 is a re-hash of all the old articles, not much new under the sun. Even the pictures are from the '70s. If you can get one of the older ones that Dean Grennel wrote, do it. It is much better having the same author, since his prose runs the same. I found the 8th and 9th editions to be a little "jarring" as a literary work, jumping between different author's styles, while the older ones were smoother, written by the same person. Bill Chevalier did an excellent job putting together the 8th edition, but it still did not seem as nice to me as the ones Dean wrote.
They basically just took a lot of reloading articles out of the magazines and put them in a book and then had Rodney or Bill write up a forward and introduction. The info is there as a manual, just hard to read as a book.