[CliffordK (OP)]

When a power tool gets hot...

Is it better to let it cool down running on low speed, no load (thus using the internal fan to circulate air)?
Or is it better to shut down & let it cool down (thus not sending power through the wires, and no additional heating from resistance)?

[Geezer]

Neither  []

You might be best to run it at full speed to help it cool down. That will maximize the airflow and it won't really increase the power dissipation because there is very little load on the motor.

[Mazurka]

The Geezer is right [] [B)] []...

The cooling effect of the fan will far exceed the heating of running at full speed with no additional load