Is getting both out of the question!?
I was in your position but with the T1 and Kindle 4. I ended up really liking the T1 (size, microsd, library checkout on device, etc) and deciding it was the one for me. But then I started missing the Amazon store and some of the deals on it...so Kindle 4 it was as well. The Kindle 4 became the cheapy "don't care if it gets scratched or damaged" reader and it tends to go everywhere with me in one of my pockets. Otherwise, I usually read on the T1 (which has my full library of books), and only turn on the kindle 4 to check out what deals on books amazon has.
So $79 to keep me connected to the amazon store and allow me to take advantage of any new features they come out with, is how I look at it.