Book discoveries, like album discoveries, happen better in stores. It's not nostalgia, but just the way the physical world works. (Think of how music lovers connected with album covers in the vinyl world.)
Just because something is "the old way" and there is nostalgia for it doesn't automatically make it worthless.
In part, I think, this is because Rdio implemented social features poorly. I find music based on the music, not on what's popular. And it's willing to recommend things off the long tail that I'd never find in a store—one of my favorites was an album from a French band that never released anything else and probably didn't make it to a single US store.
The same isn't quite as true for bookstores, perhaps because popularity plays a somewhat smaller role than for music. But I could still see online recommendations being better for depth, especially if I wanted to dive deeply into some genre and explore obscure authors that never really made it.
For me, Spotify is the best way for me to discover new music. Usually through the thematic aligned playlists or unofficial playlists curated by other users.