I upgraded from K9U to 11. Most of what I use was still in K9U. I'm not sure what other software you have, however. 
 
My paradigm may differ from yours as well. I use one piano VST (Ivory 2.5 American Concert D), for example, and one electric piano (AAS Lounge Lizard 4), because I want my originals to have that sound. I tend to gravitate to one VST for a lot of what I do, replica-wise. Things are so good imitatively that I doubt many are able to pick out the synth from the real in a recording. I've also fooled people with trumpets, trombones, and saxes from Sample Modeling.
 
 
 

I went from K10U to K11 mostly for Una Chorda and Form. Add the acoustic guitar if you need that and India and Reaktor 6 it's $20 each. Easily worth that.

I was kind of disappointed by KU11 to be honest. I got much more out of the upgrade from 9 to 10. Una Corda is good, and I am stoked to have Reaktor 6 and Blocks which is amazing, but apart from those I feel like NI has been losing its way. They seem to be concentrating on cinematic libraries which are of limited use unless you make soundtracks, and "gimmick" synths like Flesh and Form. Flesh feels like some novelty iPad app, and Form is full of awful metallic sounding presets which seems to be par for the course for whomever designs NI's presets these days. They seem to have given up making workhorse synths like Massive and FM8 (both of which could use an update) and there is nothing new in the way of effects. Previous versions of KU have been far better. I kind of wish I'd skipped it and just paid $99 for the Reaktor update.

BassDaddy
I went from K10U to K11 mostly for Una Chorda and Form. Add the acoustic guitar if you need that and India and Reaktor 6 it's $20 each. Easily worth that.

I kill you.

I went from 10U to 11U when they had a sale.. think it was about $200... very happy as I still haven't explored it all.

I'm not really feeling it; I also have K10U, and yet my most used instruments are 3rd party kontakt instruments, and a few of NI's, such as Session horns pro (which was NOT part of ultimate, I think I bought it separately), Strings, and a few of the Scarbee instruments, which again are Kontakt instruments and not part of Komplete. I don't use the EFX or the stuff that others mentioned in this thread. If they had put the full version of Symphony Horns and Strings for that price (lol) I would probably go ahead and do it. But not now.

I'm going to wait for Kontakt 6, I think. Nothing super interesting in 11.

There seems to be a flaw in the way they are marketing Komplete. I mean, we don't completely get Komplete when we update it as a whole package. They add a few extras and call it a whole package upgrade. Just doesn't make sense to me.
In reality, the package is basically the same with a few decent add ons every time. Why not send regular updates for Komplete and sell the add ons as ............add ons?
 
You're still buying it that way, but they make it appear you're getting another new improved Komplete. Am I wrong?
 
 

thepianist65
I'm not really feeling it; I also have K10U, and yet my most used instruments are 3rd party kontakt instruments, and a few of NI's, such as Session horns pro (which was NOT part of ultimate, I think I bought it separately), Strings, and a few of the Scarbee instruments, which again are Kontakt instruments and not part of Komplete. I don't use the EFX or the stuff that others mentioned in this thread. If they had put the full version of Symphony Horns and Strings for that price (lol) I would probably go ahead and do it. But not now.

Hell yeah

Personally I think it's about time they diversified Komplete into a couple of different versions. It's clear that a lot of their recent releases have been geared toward the movie/video game scoring industry and would have little value to your average music producer. The name "Komplete" is clearly a marketing angle to imply that what you're getting is a "complete" set of tools for music production, and with that in mind it's a bit of a struggle to understand how a library of Balinese or Indian loops fits into that description for most people. It's the kind of thing you'd probably use as a novelty in one song and then lose interest in. It makes more sense for TV/film scorers. 
 
Similarly, there are a lot of things missing which would make a hell of a lot more sense in a "complete" package for musicians. Like a library of piano/bass/guitar riffs (Scarbee Funk Guitarist and Strummed Acoustic are OK, but of limited use). And it could definitely use some more "everyday" synths - at one time NI were making great all round synths, but nowadays they've been overtaken by much better products such as Sylenth and and u-he Diva. Their workhorse synths are looking very dated now. And they seriously need to update Guitar Rig as well, because that is being left in the dust by other amp sims. 
 
I'd love to be able to choose between, say, Komplete "standard" and Komplete "scoring" versions. Or heck, even a pick 'n' mix system whereby you get to put together your own version from everything they have to offer, up to a prespecified limit.