"...biases and placebo have been understood in science for decades."They have been noticed and accepted, but not all have been fully understood.
At the same time, if someone feels there is a huge improvement in whatever they do to their amplifier, more power to them. I would not want to clean all the dust that settles on what used to be covered. That dust may negatively influence the sound and negate all the improvements gained by removing the cover.
I still do not understand why a person simply would not buy a better piece of equipment to begin with. Who has time to unscrew the cover, store the cover, clean the dust, and maybe something else?
Do iPhones work better with different covers?