Hi Vanessa:
I like the way you think. September may seem like a long time away, but planning, reading, and surrounding yourself with all things Disney can help fill the gaps between Disney trips.
I have all of the major Disney books you mention as well as all the other "usual titles" that you already seem to own. However, due to my work and child care commitments, I find it difficult to set aside time for reading lesser-known Disney titles. So, I find podcasts to be the best way to satisfy my Disney mania when I'm away from the parks. I'm able to find time to listen to Disney podcasts during my commute to and from work and on my headphones at the gym or while running and training for the Disney half-marathon.
Since your question specifically relates to books, I have to consult with a Disney book expert and fellow Moms Panelist, Erin F. I have seen her vast Disney library collection with my very own eyes, and all I can say is "WOW." She has a
wonderful breakdown of Disney-related books
here.
I will say that no Disney Book collection would be complete without The Complete Idiot's Guide to Walt Disney World by our very own Moms Panelist, Doug I.
As for podcasts, there are podcasts of all different lengths and for all different tastes. Some funny, some informative, some trivia-based, some trip-planning focused, some with interviews, some with reviews and some with a mix of everything. While not an exhaustive list, a few of my favorites are Be Our Guest, WDW Today, WDW Radio Show, Inside the Magic, All About the Mouse, Five Minute Magic, Dis unplugged, and Magical Definition. If you'd like more information on podcasts, a topic I can talk about for hours and hours, please feel free to follow-up with another question.
Enjoy your third trip.