It might be possible that BC actually will increase royalties to an author. Lucky person finds free book; lucky person likes book; lucky person goes to bookstore or website and purchases another title by same author. The lucky person could, of course, also go to the library, but each individual "check out" doesn't put a nickel in the author's pocket.
I, too, have looked at the books registered by other BCers whose tastes are simpatico with mine and have sought out those titles at my local bookstore.
Also, I think that the value of BC goes beyond getting free books. The friendly PMs in response to posts, willingness to be in contact with someone from anywhere simply because they read and participate in BC. Exposure to ideas. I could go on, but I won't. I'm not one to boycott authors, but if I were, I'd take a pass on Susan Wittig Bayles mysteries. In her case, I'm not picking up her books because I just don't read books about the most misguidedly glorified profession, professional extortioner, um, lawyer. Hey, come to think of it, I bet I know why she's griping about BC!