I've noticed slightly lower EGT's with my 24-valve intercooler... .
It's a HUGE pain in the butt to get the old one out and the new one in... with the radiator still in the truck. It can be done, but it's a pain.
The 24-valve intercooler is taller than the 12-valver... . more surface area for better cooling.
Is it worth the bread if you have a perfectly good 2nd Gen. 12-valve intercooler... . short answer: No. But if your IC is bad, it's cheaper to buy a 24-valve IC from Piers than it is to get an IC through the stealer... . ($895 vs. $550)
Matt