I agree that with components that have any analog circuits in them (and almost everything does, somewhere), conditioned power can make an audible difference, which is even likely to be an improvement. Unless your normal power is just horrible (eg brownouts, etc) the difference is likely to be somewhere between slight and non-existent, but there is a real scientific basis for improvement at this level. A proper power conditioner CAN make up for many of the weak links in the power chain. Digital circuits can also behave badly if afflicted with a VERY poor power source.
That said, power conditioning is not something I would normally spend huge sums of money on, but I do believe in at least surge suppression just to increase the life of the equipment.