Love the faster processor, HDMI out and better Safari performance. However, the main reason I'd upgrade my iPad would be for better resolution. Going from my iPhone 4, the iPad's screen just looks like crap. I primarily use the iPad for reading websites and Instapaper, and my guess is that I'm not alone.
Why would you buy the new version of any product only one year after you bought the last version? That seems just crazy to me.
Apple kit holds its value very well, as you would expect from a product that is selling almost as fast as it can be made. Gazelle.com is currently offering me 60% of the retail price of my old iPad. Must... resist...