K10 is a great package, I think. And the price is right. The audio demos of the new pianos sound so good, it might be worth updating just for those.
Not sure I'd pay the hefty premium for K10U, though. For me, the extra stuff would be hard to justify, although it would be different for someone into film scoring, I suppose.
I'd be interested to hear from anyone contemplating going from Komplete to Ultimate. What's in there that interests you?
Cheers,
Eddie