My testing was done with a K&N filter in place of the factory one. Say what you will about them but the fact is that for the purpose of this test, it made no difference what filter I used, as long as it was consistent.
While the car is in motion, the majority of the air in the engine area enters through the radiator, where it has picked up some of the heat. So quite simply, if you feel the gains from a 'free flow' filter solution for your tiny little stock engine is going to counter the loss from increasing the temp, then go ahead and do your thing. If you want to salvage and scavenge every last available horsepower from your stock engine... then do whatever else you can, and leave the snorkel and factory cold air intake alone until you can install a better, cooler system.
So who's going to heat wrap their factory intake first? Drop the intake air temp to as close as ambient as possible, and gain 2% you'll never get any other way...