This is an old thread with a lot of good SpectroMagic information, also.
I have seen at least one or two long-exposure Spectro shots but it's been a couple years. I tried one on my Jan 06 trip and was unhappy enough that I haven't tried it again since! I will probably try again sometime. The spinning floats may work best for such a photo.
As for metering... IMHO, it depends on the look you're going for. My best shots have been ones where I've added some positive exposure compensation, otherwise you tend to get good lights but a lot of darkness. I prefer to risk having the lights slightly blown out in order to capture more detail in the darker areas. This has worked quite well for seeing the performers themselves well without "revealing" too much that you're not supposed to see.