i like the sound of double tracked main vocals. i mix em down the middle and not always at the same volume. I'm also not that worried about them being PERFECT.
I don't think they sound good on a lighter arrangement, although, on a track we did that was just acoustic guitars and 1 main vocal, it sounded eerie with double tracked mains over two acoustic guitars. We ended up keeping the dbl tracked version
I think there's a 1000 different ways to do one thing, and they all might end up sounding great in their own right, depending on the overall sound of the recording. One thing i am finding is that when we stumble on a new sound, or a creative way to record a "same old same old" instrument, it's almost always impossible to replicate it once we've done it.
That makes me smile. It means i should always be looking for a new way to do an old thing.