I've liked the idea of book collecting forever. The problem is that I there are many books I want to read, and have to buy, so I just don't get deep in. Not like imatlas.
Like Kai I collect along interests. In my case not much worrying about 1st edition or even about hardback vs trade paper.
So I'm pretty deep in ancient Greece, the beginnings of the science revolution, bronze age civilizations like the Minoans and the Mayans, cosmology and deep time, how myth works, great explorations. Its more like a research library than a collectors library. Then, that is how book collections work.
There used to be a great catalog maker: Michael Thompson Books from Los Angles. He'd send out a catalog titles One Hundred Books every month or two. Each of the books had the detailed book description paragraph, then a paragraph on why I should care about this book. I loved these; I have something like 20 of them. But I haven't seen one in a couple of years; half a decade. His titles were a combination of the history of science, art typography, beautiful bindings, early literature. A typical book might have been: JJ Thompson, The Corpuscular Theory of Matter, London, 1907, $450. I miss these catalogs; more to the point, if they were coming out now I'd be buying many of them.