That is a serious sewing machine; I like it!

Upgrading the motor as recently mentioned is a great idea. I would advise though getting a complete motor package that includes motor, controller and foot pedal like EujeanKilt found. Finding a great deal on just a 'servo motor' is not enough. The problem is that there are may kinds of servo motors (AC, DC, brushless, single phase, three phase, stepper, encoder feedback and so on...). Not all of these motors are suited for residential power (as in 120 VAC). Moreover, the motor controller alone can run many hundreds of dollars and be a real challenge to wire.