The main reason I don't think amps should ever be plugged into a power conditioner is that I enjoy having them repaired after lightning strikes.
Packing up my 60 to 150 lb. beast, putting in the car, paying for shipping, waiting on the techs to diagnose and get me a repair estimate is something I really look forward to.
I especially look forward to getting a temporary amp, hauling it into my rack or it's place on the floor and then removing it and replacing it with the repaired unit.
Putting the repaired unit back into my rack makes me feel like I just got a brand new amplifier, and yet I only paid half that in repair and shipping bills!!
A total win in terms of money and effort for me.