Well here is the
propoganda, sorry helpful FAQ
http://www.native-instruments.com/#/en/products/producer/kontakt-5/?page=2523 I don't think its a valueless upgrade, but its of little value and potentially problematic
to me.
For me there are a few annoying things about Kontakt 5. The first is only Windows 7 is supported. It understandable that XP support is being dropped but I would have hoped for a bit more time before dropping Vista. Having said that it does seem to work OK on Vista and XP for most people, and I have the Kontakt 5 player working fine. However I am very reluctant to buy software that is officially not supported on my OS. I am reluctant to upgrade to W7 until replace my DAW.
I can understand why new instruments, like Studio Drummer and George Duke are K5 only. They use the new features, like the MIDI file support for grooves and the Time machine, but why can't you buy K4 versions of the older libraries that worked fine in K4. Yes I know they will work in the K5 player, but see my comments above about Windows 7.
Time machine pro does look like a impressive new feature, The demos's of "George Duke Soul Treasures" show it off, BUT it's one I am unlikely to need, loop based libraries don't really appeal to me.
Extra effects? OK , but most of the time I use VST effects in Sonar. There is new 16 channel bus system, fine if you want to use only Kontakt's built in effects.
I am staying on version 4 for some time yet.