Also is it possible the code i am using just doesn't take full advantage of the torque the motor is capable of my micro stepping or properly using both coils
No, micro stepping produces less torque not more.
or maybe even 32vdc (max for my chip without running 2 chips parallel).
Alarm bells - I think you are fundamentally misunderstanding something here. Running two in parallel can give you more current not voltage.
I was wondering if I could get more out of it just by bumping the voltage up to 12vdc
Yes you can get it to go faster with more voltage. However there will be more current and the motor will get hotter. The way round this is to use a limiting regulator that monitors the current and cuts off the voltage when this is reached. Then you can over voltage the motor for speed without over heating the motor.