You can avoid some hassles just by returning it to stock before bringing it in. It may not void the warranty, but the dealer may not want to work on certain problems until it can be shown that the problem exists when stock. After all, it's not the dealer's job to make your car happy with your mods.
An intercooler does help drop the charge temp (it's main function). Whether it's a 20-40 degree difference before entering the turbo or not via CAI, the intake charge is still getting heated up substantially, hence why a good intercooler is better than a CAI imho.
Most of the cold air intakes I've seen sold for these cars are really, by definition, short ram intakes. Although the proper use of a heat shield goes a long way into making use of the cold air coming from that side of the bay as opposed to the hot air of the rest of the engine bay.
And yes, a CAI can arguably void your warranty depending on what caused the issue in the first place and if the problem can be traced to the modified system/part. If I remember right, the Magnuson-Moss Act covers aftermarket parts on a vehicle causing the warranty to be voided, unless your warranty specifically states ANY modified pieces will cause a void and you signed the contract anyways. Then you get into a legal grey area. The fine print is the final say essentially, unless of course the dealer can prove without a doubt that the part caused the issue being repaired under warranty.
I agree with the above posts. Intakes don't do much for these cars and for other manufacturers they will void warranties for certain ones under the condition "Turbo dusting" or the way they are constructed the maf is skewed causing a lean condition. Of all the mods that you can do, intakes aren't that hard to go back to stock for warranty work. Which takes longer to do, remove an intake or letting a car sit at a dealership for days because they are trying to actively get GM to justify not working on your car and stick you with the loaner fees if you aren't in that group of people not old enough for a loaner car?
Am I saying don't get one? Nope. You do what you wish to your car but remember if you want warranty work done you have to give them the same car they sold you to fix.