Besides the aero fastback additions, the front (nighttime aero) could be made cleaner with a flush mount headlight kit. The OEM units & the pop-up motors deletion could have some weight savings as well. Smooth underpanels. A black coroplast grill block fill, only non-track commuting days. Passenger side mirror deletion and driver's side F-1 style aero side replacement mirror. Rear antenna deletion/flush replacement. Because of the front tires' open exposure to air stream, some have experimented using the OEM mud flaps, in FRONT of the wheel well position to some degree of Gurney flap improvements! There sooo many body kits purporting to be aero. Don't know have a clue of real good one, except for one real pretty nose, like this...
http://ep.yimg.com/ca/I/gomiata_2125_105339649
I'm sure many more contributions will be added to your thread. Additional notes:
Mazda Miata COMPLETE Flush Mount Headlight Kit
http://www.mmmiata.com/images/products/MM147-BRAP1.jpg
http://cgi.ebay.com/ebaymotors/ws/eB...m=220677781212