Alright, here's my opinion...
I believe that 'Discotheque' has, and always will be, about the production of the song, itself. In essense, the production is the song, and therefore is what makes the song. If you strip 'Dischtheque' right down to its bare bones, you really have nothing but one good guitar riff. There really isn't much of a melody - (Have you ever tried humming the song? It's frighteningly difficult.) - and there isn't really much of a hook. To be perfectly blunt, it's one of the worst written songs U2 have ever put out, simply because so little actual song-writing went into it. (How can something be well written if there really isn't any writing, right?) But before you all flame me, that's not necessarily a bad thing. As I've already said, what makes the song is the production. Unfortunately, U2 have decided to strip that production away, and expose the song for all of us to see. Unfortunately, there really never was much there (underneath the layers), and now U2 have removed the curtain. I think I know why they did it, though. Right now, Edge and the band are into "primitive guitar riffs" and minimilistic aproaches, so they wanted to turn it into a simple rock tune, and retain some of the swagger that it was originally about. Unfortunately, Edge forgot the song didn't have a solid foundation. Oh well. I hope the next album does. Judging by 'Electrical Storm' I think it will. I just hope they don't go too simplistic.
The short answer:
The layers are what made the song in the first place, not the song-writing, and that's why I much prefer the original.
On a side note, a song like 'Stuck', for example, didn't need to be heavily produced, as the song-writing is very good. Just listen to the acoustic version for proof.