My ultrasonic cleaning tank piezo gets warm, without solution it'd proabbly melt, but I think thats a parasitic effect.
If you upped the voltage enough I spose heat would be generated, life of the buzzer would go down too.
The circuit in post #4 can be made to drive the piezo as hard as you like, the inductor will apply a voltage to the piezo to equal current through it at switch off equal to inductor charging current, the tranny has to be capable of standing off this voltage which can be 100's of volts.