I don't think a lossless re-release of a 1972 mix will be much better than what would have been heard in '72, give or take a toke or two. A new 5.1 mix, even in lossy DTS/Dolby Digital *should* sound better.
Recentle I listened to the original Tarkus stereo CD, the new remixed STEREO CD and same mix on DVD-A. By far, the biggest jump in sound quality was from original stereo CD to new stereo mix CD. On casual listening I couldn't hear any difference between new stereo CD and new stereo DVD-A.
Totally agree- the mix is so much more important than the format. One of the wildest surround mixes I have is FL's Yoshimi- sometimes I choose the bleep blop waveforms- or whatever they call them- in the extras menu so I can have a visual feast along with the sonic one. Even though it's only DD, it stll sounds awesome and I can't say I hear a difference w/ the MLP layer; it may be there, but not significant enough to notice. Of course, my understanding is that as the # of channels increases, the less resolution is needed.
Regardless, I try no to get hung up on formats; if it sounds good (or great), that's all that matters. I'd rather have a lossless quality surround mix of an album than a pristine, highest resolution copy of same in stereo. It's all about the mix, and to me, a good mch mix beats a good (or great) stereo mix. But that's just me. YMMV