Hmm. That's a tough one. Platinum is a great upgrade but for your purposes probably not an essential one, as X3Producer is a pretty full-formed DAW in its own rite, so quite possible your money might be spent elsewhere. But it seems to be getting better and better, and remember you can always jump in on a monthly plan any time they release something that seems essential to you.
Rapture Pro is a great and full-featured flagship for the money, but does seem to have some teething pains we're all waiting for the Bakers to attend to. Hopefully soon, but just so that you know. There's potential there, and a ton of sound for the money (not so much that much that you don't already have in DimPro and Rapture, but more potential for deep tweaking esp on the Dimension library) but it's a wee bit wobbly in its current incarnation.
I have the full Komplete 9 - not Ultimate, just standard but even so it's an amazingly deep package, hard to imagine running out of possibilities. If you need a new controller you could consider the Komplete Kontrol series, which interface with it beautifully and have pretty much the best synth-action keyboard feel I've ever played. (Even without the keyboard, I'm finding the Komplete Kontrol software a nice environment for quickly finding sounds I have in the library but might otherwise never have stumbled on - but still being able to tweak them deeply.)
Or you could wait a bit for the Akai Advance series to drop - similar deep hardware-software integration but not as tied to the NI stuff (still seems to work well with it though, from the walkthroughs I've seen) - I've heard NI is opening their platform up as well, but that depends on other manufacturers supporting it, whereas Akai seems to be doing a lot of integration out of the box. I've also heard they have a great keyboard feel but again, non-weighted. I need hammer-action keys for some purposes, but your mileage may vary...
Z3TA+2 is a great upgrade from the original, but much in the same line. If you liked the original, it's more or less a no-brainer, if you didn't use the original much then maybe not.
Not sure if that's helpful but it's hard to really give you a "you should definitely do this" kind of answer - everyone's purposes, needs and budget are different...