With all that fine mist the beamshow effect could be fantastic.
But you need an FM transmitter so that people can tune in to some music to go with the show. (I hear that all that water falling makes a bit of noise so no sound system would work...) But slip some headphones/earphones in to help with the loudness of it all and find music to accompany a laser show...that would be something to see.
How about a "flashmob" sort of thing ?
A couple of people bring projectors, (cause the falls are rather wide so at least 2 projectors would be needed) you can get a small battery powered FM transmitter for about 20$, a laptop source of course with the show and music, and the toughest part would be power. Maybe some local outlets are along the edges or in the landscaping or even an inverter with a car battery in a baby buggy(to hide it) sort of thing.
5 people meeting, connecting, then blasting a show out for 5 minutes only to break apart and disappear back into the crowds. -Use a graphic to show what frequency to tune into at the start and maybe have a couple more people with potable radios that just happen to be in the crowd to tune into the signal and play it out loud for the few people near them...
Bet the video would be online within minutes of it happening...
And you could do it more than once too.
That would be something to see alright.