On the topic of "roof scoops", I'll post a functional one for the Miata crowd.. instead of feeding the engine, it's for the driver though, haha. (no joke) Any who've driven one on a hot day can probably attest to how hot air seems to stay in the footwells, even with the top down and @ speed. Don't have any pics of mine mounted so I'll post one from the website. They're definitely worth the coin though and pop on/off in seconds. 
http://www.coolbreezescoop.com/servlet/StoreFront
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http://www.coolbreezescoop.com/servlet/StoreFront