Danny,
If you're gonna cool the water anyway, why not place the DE's closer to the surface of the water? I personally think that one of the main reasons people don't use DE more often is simply because of one reason, and a consequential effect of that reason. The heat thing is an issue, period. It can cause alot of troubles that unless you adequately prepare for, can wipe out your tank. Since its a hassle to think through potential problems, (not just here, society as a whole. And I'm just as guilty as the rest of the planet, so please don't think I'm climbing up on a pedastal...soap box maybe, but no pedastal
), most people will just go with whats easier. Since most people will go with whats easier they generally gravitate towards mogul based bulbs/set-ups. Since this is what most people do, there are more options available in mogul/SE bulbs. Consequently, since there are more options available in the SE/ Mogul range, then more people will gravitate towards those choices...vicious cycle...rinse, wash, repeat....
to be honest w/ you. I've only recently purchased an HQI/DE set up. I will have it up and running (hopefully) here shortly, and I will be able to give you guys my personal experiances. I am planning on having the tank run w/ just rock in it for a few months prior to placing in any corals. This will also give me time to fine tune the tank, and deal w/ any instability or heat related issues.
Nick