I think the fundamental flaw of SoC is that it pretends to be something it isn't. SoC is no more "organic" or "spontaneous" than traditional narrative methods. It pretends not to be stylized, but, of course it is; there is no escaping that, and to attempt to, is futile.
That said, "Sound and the Fury" gains a great deal in power through its usage. But, ultimately, the greatest power is that it contrasts the different streams. If the novel utilized only one of the streams, instead of the 4, it wouldn't be nearly as effective. So is it right to say that its power derives from SoC? Or that its power derives from (for lack of a better term) its composition as a cubist composition?
For me it's the latter. But the SoC heightens the contrasts. If all four were told only from a traditional narrative standpoint the contrasts wouldn't be so stark.
It's definitely not my favorite technique. But it has its virtues, and its weaknesses.