That air is moving way to fast for heat soak to even matter, if the air was trapped and standing still then yes. CAI, are just for aesthetics, drop in filter and you stock tube. Or you can do the preventitative maitanance mod! Some of the hard stuff you will not need to replace till another 100,000 miles, just food for thought!
The heat soak may not make a giant difference, but why ignore it? Metal will clearly allow heat to transfer to the intake charge at a faster rate than plastic will allow.
I do agree that at N/A power levels, a CAI isn't helping, plastic or metal.