I'm dubious of the benefits of grounding the TB's. Maybe if you had an existing wiring problem with the throttle position sensors and/or actuators in them or something. Seeing as how the TBs aren't naturally grounded (connected to plastic intake), I'd imagine they wouldn't bother having the body of the sensor/actuator ground out to the TB to begin with (meaning, grounding the TB may do nothing electrically regardless), but I have to admit I haven't pulled the sensor/actuator out and looked.
The only thing less reliable than a butt dyno is a butt impression of gas pedal responsiveness issues
