A couple more things you might want to consider. I see you're using a 5D. On your LCD screen, scroll down until you see the Custom Functions menu. From there, go to Custom Function #14, and make sure you set it to Average (the default is Evaluative); this makes for much better flash readings in dark rooms. (there's been some debate about that, on this forum, but after having shot 100+ weddings with a 5D and an on-camera flash, I can tell you that using the Average mode is excellent for indoor shooting!).
Secondly, about bouncing your flash. Yes, bounce flash is much better light than direct flash. However, if you'll be bouncing it off walls/ceilings that aren't white, you will get a color cast. This is when you might want to get some kind of bounce card. Even rotating the flash head so it points up at a 60 degree angle, in combination with the small bounce card that pops out of the 580EX units, is better than bouncing the flash off the wall behind you if that wall is dark brown.
The disco lights sound kind of cool, actually. You might try setting your 5D to Tv mode, around 1/20th of a second, and dialing down your flash by 1 stop. This will make for some interesting lighting as the ambient light from the disco ball (or whatever) combines with the light from your flash. For example,
here's a trick you can try when you're shooting the dancing and you feel like you've exhausted all the standard shots:
Again, set your 5D to Tv mode at 1/20th of a second. Put on your 24-70. Make sure your flash is on (bounce it if you can, even if it's just bouncing against the bounce card attached to the speedlight). Compose your shot with your lens at 24mm. At the exact same time as you push the shutter button, zoom the lens all the way to 70mm. Look at the resulting image on your LCD screen and you'll see what I'm talking about. You can play around with the settings after that first shot, to get it just the way you want it.