More expensive drivers can of course support larger stepper motors, but the biggest advantage is that they have more sophisticated control algorithms.
The newer digital drivers are completely silent at almost every speed, and have much better low speed control.
Noise and humming from stepper motors is generally indicative of resonance or wasted energy which can impact the motors temperature and the surface finish of your cuts/prints.
The cheaper 3d printer electronics did not exist when the 2.x design was made, and will do a reasonable job. I believe the lasersaur design uses the allegro chips .
I'm planning on using these for my next project:
http://www.omc-stepperonline.com/leadsh ... -p-75.html