For several years when I was a kid, my father and I would plant, nurture, and eventually harvest a big vegetable garden. It was something special he and I shared—my one older brother still living at home didn’t really take to it; my mother helped, but she focused mainly on her flower gardens. It was Dad and I who planned the vegetable garden, plotted its layout on graph paper late each winter or early in the spring, and did most of the work. Now, umpteen years later, Dad still grows a garden each year. When we catch up by phone or in person, I get an update on how everything is doing—what’s growing well or poorly, what’s been affected by the weather, and what’s seeing a good yield. How do you measure the grassroots health of a hobby? I’ve always felt that the number, depth, and quality of books, magazines, and other products that serve a hobby (like coin-collecting) make good measuring sticks. These are better gauges than just looking at auction records and top-end sale prices. It’s...