I can believe that any instrument (that uses tension to adjust pitch) tuned slightly lower can sound "nicer" simply because the instrument is less strained mechanically, and the overtones (which are never perfectly intoned due to the instruments construction) will be lower in volume. One reason why concert pitch was standardized in the first place was pitch inflation: musicians would tune slightly sharp to sound brighter and more exciting than their rivals. Soon singers were complaining that their voices were being forced out of their natural range...
The negative effects that the 432hz proponents ascribe to the 440hz standard actually do exist, but the cause is not the absolute pitch but the relative size of the intervals... Equal temperament is a compromise to allow concert instruments to play in any key without retuning. Notice the frets on a guitar are positioned at equal proportions. Mathematically, the fractional pure tone values do not fit into these proportions, so the result is that many harmonics are, by design, out of tune by tiny amounts, even assuming the instruments are mechanically "in tune." Composers and musicians know about these "wolf intervals" and avoid the worst of them, but they are always present in an equally tempered environment. However, musicians who play un-fretted instruments often learn to play with true intonation as much as possible, but on a piano for instance this is not possible... An alternative is to have moveable frets like a sitar, re-tuned every time a new key is played.
The constant low-level dissonance of equal temperament can have an invigorating effect on the mind and body, but it can also create stress and fatigue. Listen to a performance with justly intoned instruments, that is, tuned to the perfect harmonics, and you will feel the difference. The effect is more calming and even trance inducing.
