As a game designer, I approached this book with an open mind, not knowing if I could pick anything up from it. It surprised me though. Although the book was written in 1987 and could use an updated version, the design principles stated there remain relevant up to today, even in a field that had been rarely touched upon when that book was written. (Yes, it does talk about games, but only in terms of difficulty level, and only pertaining to D&D.) In particular, the game designer could look at the Seven Stages of Action to see if her game is performing up to par on the usability front.
You might not find anything here that is imemediately useful in your design work, but all designers worth their salt should broaden their horizons and continuously search for things, both new and old to be able to use in their craft.