I'm currently running a Cooler Master HAF 932 case, 3 HDD (2x 1TB and 1x 500GB), 2x GTX 285 GPU, and an i7 @3.2Ghz with a Xigmatek Dark Knight CPU cooler. Would I see much of a benefit if switched to water cooling?
I've got a similar setup to yours that I'm building and I'm doing watercooling... you could see a nice improvement from just replacing your current cooler, though. (I have one that's doing a just over par job on my AMD rig) If you're an aesthetics + "look I have something extreme" guy like I am, I say go for it.