(9/17/2018) Tim Thompson turned me onto the
Morph touchpad from Sensel,
which, besides being pressure sensing and solidly
built, has a built-in accelerometer. This gives a way to lift the touches into 3D, makes for a more expressive controller. Simply lifing the pad and tilting and shaking it gives more for the audience to watch in performance as well, escaping the usual "person on laptop turning knobs" scenario.
I'm also finding the experience of directly expression via touch qualitatively changes the feel of playing. I have a lot more to do with it, like connecting the accelerometer in with my physics simulation, using position/pressure/acceleration for various parameters like color, size, speed, etc. Tossing objects into space would be cool, too.