I thought long and hard about it before making my decision. I couldn't find any documentation (that I believed) that wasn't published by someone who makes their money selling parts. But I still bought and installed the Airaid MIT. I figured, heck, I like the sound, and if it gives me .1 better MPG, that's great. I can't say I feel any gains with my butt dyno. But I like that I can hear it when I go to pass someone on the 2 lane county road.
I put a K&N intake on my old '98 K1500 and I swear with that & a flowmaster muffler I gained 1 whole MPG (with years of gas mileage calcs to back it up). That was a generation ago when trucks didn't roll off the factory line with every drop of fuel economy squeezed out of them. Can we really free up some HP by simply removing the restrictive air chamber? Maybe. Sound reduction is very important to the manufacturers, and the small increase in noise with a CAI is worth it to me.
At the end of the day, do what makes you happy.