Double-track!!
My two cents: Duplicate only if you can't get the kid to play it the same. If the tracks are off by too much, due to sloppiness or eternally changing riffage, it'll sound like fuzzy mud.
Duplication doesn't work so well, but it works a little. If they're not perfectly aligned though, it'll get a chorusy effect. Panning to opposite sides with delay gives, to me at least, a cheesy fake stereo sound. Good for an effect IMHO, but I wouldn't do it for a whole song. It also prevents you from having a separate guitar track in each channel, which sounds better for metal etc. than having essentially mono guitars (even if panned and delayed).
The way duplication worked best for me was by taking the duplicate and compressing the living crap out of it, adding some EQ to taste etc., and mixing it back in under the original track (a cheap variation of the "exciting compressor" technique!!

)
Lately I've been trying out recording three guitar tracks--each with a different tone-- per channel (a total of six). Ferinstance, a
Marshall sound in each channel, a Mesa sound in each channel, and a stompbox sound. It's the beefiest thing I've tried yet. But I'm trying to get a 'heavy" sound, so this might not be what you're looking for.
