The main difference are maybe that CZ sounds a lot more analogue and lofi but the programming is much easier than in VZ which is harder but the sound is quite opposite, very hifi, glassy studio but warm at the same time. VZ is much more menu-driven but in other hand it contains a big matrix lcd screen showing all the details like actual envelope and lfo curves.
VZ contains a lot more performance options than CZ. Of course the CZ-1 contains velocity and aftertouch as well, but however VZ contains also a lot of different possibilities of complex multitimbral layers and cross-fades across different sounds and performance features. I think VZ is much more capable as expressive synthesizer than CZ when programmed right. Don't forget VZ contains 3 wheels (1 pitch and 2 programmable modulations)