I plan to approach this incrementally, but it's a clever idea. I'd say that once the list is bigger, a lot of fun new features can be implemented. At this stage, I favored the essentials, trying to get the minimum viable product out there.
I totally agree with that approach. Just signed up, and can't wait to start getting messages.
Another interesting idea to consider might be some sort of integration with librarything.com, delicious-monster.com, or something along those lines.
I hope you're, at minimum, collecting some sort of data on how many people click through from the emails to get more information on the books, seems like that could be very useful and help you justify and build more features in the future.
