Well, to me acoustic music played on string instruments (guitar, bass, piano) is the real music, and the electric stuff is optional. Obviously the reasons to play songs electrically is to project volume and increase the textures possible in the music. This is not necessary (though it's often great!) in most of U2's songs since they're such solid compositions.
So, I would love to see an acoustic-only gig; sort of a one-off "unplugged" thing. Larry could play some bongos or whatever, and the other three just do the usual thing. As long as Bono doesn't start hamming and posing too much, it would be fantastic.
What I can't stand in simple, lyrical R&B/rock/pop/blues compositions is 40-piece orchestra-overblown arrangements. So, let's have just the four guys onstage with an occasional violin or keyboard help.
I agree that "Drowning Man" is brilliant, by the way. But I think the violin gives it a lot of its character --the chords of the song are standard and appear in about 500 other famous tunes.