I've never messed with IAT much, but I think the gain would be minimal. I remember reading an SAE paper that said it affects power, but that was in big rigs pulling lots of weight under 50-80% load. Heck my 89 Dodge gets 25+mpg with no intercooler at all (didn't come with one from the factory) if I keep my foot out of it. If you're looking to get stupid mpg, I'd check these guys out:
DeLuca Fuel Products
Website doesn't look like much, but the guy knows what he is doing.