I agree with most of the positive remarks about acoustic music. It's probably just me, but a lot of the time I seem to find acoustic music more interesting, refreshing and passionate if I have only ever heard the polished and slick produced versions of them first. When I hear the acoustic versions second, it seems, most of the time, to reinforce the feel (as somebody said earlier) of a more closeness than the original recording, and it is great to hear a decent tune from a different angle.
I think what many people overlook is that many 'decent' (subjective) songs will derive from an idea originally penned from the acoustic guitar anyway. My old lecturer used to say, 'shit in, shit out', meaning that if you've got a crap record, no matter how much you polish the 'turd' (mix it with as many effects and techniques as possible), it's always going to sound like a turd. So, if you strip down a 'decent' studio produced song, it will usually, more times than not, sound great acoustically too.
Anyway, acoustic does not neccessarily have to mean completely stripped down. I have heard remarkable sets where they have used orchestras to give it even more emotion and depth. Whether you can really call this acoustic is open to interpretation though, I suppose.