Not seen it on SUs but have on turbo'ed cars. Get a kit from www.coolingmist.com, however, these are based on MAP pressure not vacuum. You would probably need to rig something up to get it to spray when you wanted it too.
I was watching one of the HP shows the other week where there took an ethanol/ water kit and threw it on a turbo'd V8 and did nothing else. I think it jumped 45hp just because it was cooling the intake down. Was kinda cool.
I've been searching for kits on CL local and see them from time to time.
You should be able to reduce detonation if you have any and or increase your timing. Unless your intake temps are really high as is, then there may not be much of gain by adding without bumping your timing up.