I'm using Cubase 9 now for a few weeks and for me the upgrade is worth the price because of the new docking feature (zones). I use to have two monitors for tracks and mixer, but with the new docking feature it is possible to place the mixer window under the tracks window. This greatly improves my workflow. I replaced my two 22inch monitors with one 27inch monitor. I don't use the other new features (yet). Together with my Steinberg CC121 controller it works like a charm!
Be carefull though with your VST plugins. Only VST3 is supported. All VST2 plugins are disabled.
Another very intersting thing to be mentioned is the new built-in sampler.
As for the VSTs: not all 64 Bits are "allowed" by Cubase 9. Some of my 64 Bit Korg Legacy Collection VSTs are blacklisted. And for those using Automap; it's not yet working with Cubase and supported by Novation....
But beside this, it's yet another step forward in terms of workflow and especially stability.