Exponential VCAs don't have to be entirely new VCAs. The Intellijel Quad VCAs can be tuned to respond linearly or exponentially. It's a matter of preferences. If you want your VCAs to respond exponentially to your linear signals... then sure. But it's up to you if you need them.
Your rack could use some utilities like attenuators or attenuverters. You have a quad mixer/VCA unit. That's fine. But I see at least five sound sources. You don't necessarily need more mixer channels. But it's something that I noticed. Another small mixer for mixing CV (or audio) would be great in here. It doesn't need to be special, just handle audio and be DC coupled for CV.
Do you have a noise source? Pink and white? Noise mixed at low level can add some grit and character to a sound, even if you're filtering off the high end.
I'm assuming that your sequencer and time based effects (reverb, delay, etc.) are all handled outside of the box.