At the absolute very least = there are so many extras, value added selling points, that the upgrade fees seem kind of negligible.
At the core of the program = there seem to be an array of features that have been asked for on this forum ie they are listening to us.
The Quad Curve EQ looks as though it has been refined, and frankly, "I can not think of a vst plugin eq, that is better than the quad curve eq in Sonar."
Colors!! We seem to slowly be moving beyond this, "gun metal gray, sterile operating room," look and feel back to the land of, "fun to look at, and easy on the eyes." Although, IMHO, I can see the GUI needing 1 more round of X tweaking to be really wicked.
I think its a pretty snazzy upgrade. I don't know if I will early adopt, but I will likely adopt sooner than later.