That's the key, most electronic and rock music wouldn't benefit much from any format upgrades. Acoustic music is the most hard to reproduce, and thus requires the best in playback technologies.
When I listen to St. Germian, it does not matter if I'm listening to it on my 5 year old portable or my digital separates sysytem. When I listen to Mccoy Tyner's New York Reunion, thats where I really know something missing from my portable and 44/16 PCM playback its self. In addition, Most jazz and classical records are produced on a much higher level than that of mainstream music, so the argument of 'the quality of the recording being FAR more important than the failings of the CD medium' becomes less relevant when it comes to those styles of music.
And as far as turntables go, most cheap and older setups suck big time. But I think you would have a hard time saying a good vinyl setup playing a Classic Records 45LP OVERALL sounds worse than even the best CD version.
Just my two cents