David Blair at Custom Power Cord Co. in Skokie IL uses heavy liberal shielding for all of his AC cords with great results; evidence that this can in fact be done to good effect when properly engineered.
Now take another look at shielding from a somewhat radical perspective: specifically, the Synergistic Research "active shielding" approach. The applied DC voltage potential on their cable shields (which are out of the signal path) is said to saturate the insulation dielectric such that it won't leach electrons from the signal carrying conductors. I admit to healthy skepticism when I first read about this unique shielding system, & was still rather doubtful regarding its benefits when I first auditioned it with some decidedly mid-fi componentry. Yes I heard an improvement with the active shielding power supply energized, but not enough difference was perceived to justify the expense.
Later on, after significantly upgrading my rig to better quality components, I decided to incorporate the active shielding system. Now I could really hear a significant difference between the active shielding vs. passive shielding; this system really does work. Proof that this effect is not just psycho-acoustic came to me a few months later, when the rig was shut down during a storm. Wife had powered the system back on the following day, but had neglected to turn on the shielding power supply (they call it a Master Control Center - but it really doesn't control anything). I came home from work & even casual listening revealed a deficiency, but I couldn't quite quantify the actual problem. Bass was lacking, dynamics were softened, highs just weren't what they should be, staging was constricted. I suspected the disc that she was playing, until other more familiar material didn't measure up either. Sitting in the living room, I was gazing at the rack & then realized that the tiny blue LED AC power indicator for Master Control Center was not turned on. Turned on the power switch & everything fell right back into place. That's proof enough for me; I'm not "imagining" these effects.
Synergistic has since incorporated active shielding into their AC cords & even speaker cables. Currently, only my Synergistic interconnects have the active shielding, but I now plan to retrofit my AC cords. I don't use their speaker cable so I can't really comment on that; however I remain convinced.