I like the potential of this app a lot. Hope you have the motivation to carry it through to completion.
A feature that would be very nice is to be able to hover the mouse cursor over a cover and get a popup bubble with the basic stats for that title. You know like title, author, price, short dust jacket blurb. Audible does something like that on their site as does Netflix. Given your goal is to make browsing more efficient requiring users to click on the title to see the details is no more efficient than the current very weak Amazon Kindle Store.
Another feature would be the ability to also show only books available from Audible. The Kindle does play Audible books so it seems a natural given that Amazon has owned Audible for more than a few years now. Amazon has integrated the Audible library into the main site anyway.
I don't know how easy either feature would be to incorporate as I am not familiar with the Amazon API and don't know what data is exposed to the developer.
Good luck this does appear to be one of the few Chrome apps with real promise so far. Some are interesting but nothing too exciting yet.