Okay help me out... How the heck does flipping over the air cleaner cover IMPROVE airflow??
My air cleaner is domed upwards on the top - like most others I've seen. Therefore, flipping it would create a SMALLER cavity INSIDE the air cleaner. This would do nothing to change the amount of surface area of the filter itself, and since most air cleaners also curve upwards on the BOTTOM plate, I would think that this would pinch the air flow coming into the top of the carb, and actually REDUCE air flow into the engine.
Cold air intakes - CAI's - perform two primary functions. They reduce the air baffles and kinks from the air inlet - these are installed by the manufacturer to REDUCE engine noise because MOST customer don't want that sound. This creates smoother air flow, and more sound. They also usually move the air inlet towards the bottom of the car to scavenge the cooler air that is flowing underneath your car. Some "tuners" even go as far as to remove fog lamps or cut holes into their bumpers to allow air flow to enter directly towards the filter.
Obviously this doesn't work on our cars because the air cleaner - the air inlet - sits directly atop our motors. The best way to increase air flow is - as Chrycho mentioned - to remove the covers for the fake air scoops in most of our hoods. My dad did that to his 'Cuda - drilled a bunch of holes into the scoops. Others remove them entirely and add screens to keep leaves out and such.
I'm gonna go on record for saying that flipping your air cleaner lid does probably exactly opposite of what you want it to do. If that were the true "high performance option," I'd think that they'd have started BUILDING them "upside down" already.
I'm no automotive engineer, but I DID stay at a Holiday Inn last night...
Jeff