You can hear the difference from the old motor compared to the new. I recorded two records to cd to listen in the car and after the motor change I recorded some tracks from both to hear the difference.

The old motor was loosely mounted with an O ring to minimize vibration transfer. Of course since the motor was able to move speed variations happened. The new rigid mounted motor was tuned electronically to reduce the motor's vibration. Now that Rega has minimized vibrations and speed stability the sound has improved. I took it a step further and bought the Rega power supply upgrade. I am not sure of this but it looks to me that the PSU is powered by a walwart that first converts the AC to DC. Then the unit converts back to AC for the motor and the speed control. I think the regenerated AC is much cleaner than straight from an outlet. Better speed stability, less vibrations and cleaner power have improved the sound of my table.

Belt drive vs direct drive is an interesting debate. In a belt drive table the belt does not transfer vibrations to the platter. A direct drive has the platter sitting directly on the motor's shaft. I think it would be easier to design a low vibration belt ttable than a direct drive table.

An interesting comment I read once is that a turntable's performance is more limited by internal vibration than external vibrations. The writer moved his table to another room and found little improvement. After reducing the vibrations and upgrading subplatter and bearing I am a believer in lower internal vibrations.