I must admit I am tempted by the crossgrade from Kontakt 4 to Komplete for 187.5 Euros, but its not compelling.
I do have concerns that my OS is no longer officially supported by NI.
What may really open up things for me is the synths, Reactor, Massive, FM8 etc. How good are they?
GR5 would be a real nice to have, but I currently have GR4 XE and Amplitube so I am not exactly hurting in the amp sim department.
K5 (or K6) is probably going to be essential in the long run but I am in no hurry to upgrade until a must have third party library requiring K5 comes along.
I have a few of the included instruments packs for Kontakt already. The remaining ones I have covered by third party instruments. MM bass and the Scarbee Rhodes & Calvi would be nice, but I am not exactly short of bass and EP sounds. Sampletekk covers my acoustic piano requirements. Abbey Road 60's Drums and Studio Drummer, well you can never have too many drums, but there are some drum products a lot higher up my wish list.
Battery - I know it has some fans but it looks a bit dated to me and I am not sure I would use it much. My drums are Superior (with several EZX and SDX) or Steven Slate with a bit of BFD Eco thrown in. I seldom use electronic drums.
So it really comes down to do I want the synths?