Pretty inexperienced with Synplant 2, but with old one I would always just move my modwheel all the way up, and it would give me 12 completely different sounds, I'd pick my favorite one and go from there. Now with Synplant 2, when I move my modwheel all the way up, all 12 of the sounds match. I've tried the different modes, growth +, growth - , etc... What am I missing here? Thank you!

You probably have loaded a patch (by default?), which has all 12 branches be identical. You might consider clicking in the middle seed so that the last touched branch will be used as a new seed. Do this, when all branches are not grown (your modwheel being down). After that you should experience the behavior you are familiar with.

Also: you can also drag the branches by itself and/or drag this dotted circle to grow branches or all branches at once. Modwheel can be linked to something else than growth. So don't get confused when in a different patch modwheel might not change the growth at all. (;