Why do we want diversification? According to a reference on the Global Issues website, "75% of genetic diversity in agricultural crops has been lost." In fact on its website, Slow Food USA maintains a list of foods, called the ARK of Taste, that are on the verge of extinction. Some examples: 'Moon & Stars' watermelon, 'German Pink' tomato, 'Crane' melon.
So as you're thinking about your winter crops, chat up the folks at your local exchange to see who's planning to grow what and work together to create a diverse harvest that you can share. But always remember, first and foremost, to pick the right plants for your climate.