I own both the first and second editions of this book. I am an amateur mathetician; I don't think there is a siginicant difference in the two editions, if you are a non-professional like me. They are both excellent books, and almost exponentially inrease in difficulty as one gets further into them. The writing is less dense, and more amateur-friendly, than Washington's other famous book on cyclotomtic theory. There is some surprising humor in "Elliptic Curves" too. Washington makes a clever pun on Fermat's marginalia. I would gladly recommend either addition---unless you are a Faltings to begin with.
charlie sanders