The problem is that there aren't that many BDs that include the same audio mix that was on the DVD.
Comparing the new mix to the old mix is not the same as comparing BD audio to DVD audio.
I will say that when comparing the same mix on the same disc, carefully trying to match playback levels (which is nearly impossible to do on an instantaneous basis), the high-bitrate core tracks rarely sound much different except in subtle ways that require careful listening to detect.
Comparing the BD to the DVD of new releases of new films, where the DVD has standard-bitrate audio, the difference is easier to detect (although again, this is not scientific and the results are entirely subjective.) But it's still not what I would call a "night and day" difference.
Whereas the difference in video quality between SD-DVD and BD is rarely less than dramatically obvious.
For purposes of this poll, I think video improvements are more noticeable, in the sense that you'd have to be visually impaired or watching from the next room not to see it. But the audio improvements are also worthwhile, although they can be masked by mediocre speakers, a poorly tuned room, or other factors.