SACD/DVD-A is transparent to CD audio for most people in most situations. (Apply the Nyquist theorem to the CD spec and see what happens.) The only real advantages to SACD/DVD-A are longer programs, more channels, and (usually) an effort by the producers to put together a better mix than appears on the CD version. But they have the disadvantage of being expensive and difficult rip -- if not outright impossible at this time.

EDIT: But HDTV is awesome, and clearly superior to NTSC DVD. The sooner we get lots of optical media for it, the better.