Sorry to say the same thing over and over again..in these threads that come up. But quite simply, any and all pieces of wire act an antenna, and there is no bigger antenna in ones home than the yards and yards of AC wire. Any audio component, well designed or not, can be impacted by RF (as well as EMI, etc..) and an audio circuit can work to amplify or pass on RF...or can intermodulate it with the audio signal. It is very true, that getting crazy with high cost AC treatment can become overkill, but RF and other electrical concerns for audio does exist...and as Jeffrt points out very well..it is best for one to try, and do, at whatever level pleases them.
The fallacy of ac treatment
I see a lot of threads related to managing and tweaking the ac powerout end of electronic systems. Much has been said about dedicated wiring, termination and even the right kind of extension cords to use. I work for an electric utility; and that's the extent of my credibilty here. The majority of you will no doubt be far more erudite wrt music hardware. Just a thought, though: domestic ac distribution goes thus: power station-step up-city-step down-subdivision-final step down. As far as the utility is concerned, you and all your neigbours are collectively the load for the step down tranformer. Any inductance/capacitance created by your neigbour running motors/tubelights, etc is felt by the lot of you. Additionally, the voltage frequency will almost always move around a tolerance from 50hz as the whole country turns on the air, off the lights - changes all the time as peaker plants ramp up etc. Nothing can change that- the frequency of the grid supplying your city is the frequency in the mains at your house. So what's my point? Well only that how much difference can the last 10 feet of cabling, etc make when the other hundreds of miles are outside of your control? And more importantly, frequency is one of the most imp parameters for measuring electricity quality (your expensive hand-coiled toroids are entirely subject to the f in the primaries) and nothing other than running an f generator can shield you from that. Methinks all the improvements you see from ac cord treatments are pyschosomatic. But that's cool.