I really love non-video games, for they are mostly pure game mechanics. Most of the time the mechanics are abstract, with a theme added to them, to make the game more appealing (more marketable?).
They are an invaluable source of game design knowledge as they are cleared of all the other layers a video game can have (visuals, story, sound, animations). A board game manual is, in this regard, like a game-design document, as the rules are basically the all the game mechanics.
Here is a very interesting article about 20 classic board games, a description of their rules, their goal, and what lessons are to be learned from them.