Well, awesome! Have you ever tried weighing you're 14" steelies? Or do you have daises or something?
A hard top may be a good addition for aero, but I can't be sure.
I'd look into aluminum ones, there is a 7-spoke hollow spoke design that is one of the lightest out there. you can find these by noticing on the back of the spoke there is material taken off, making a spoon shape on the inside.
You could switch your 5speed for a more fuel-friendly 6speed, which also has a better power holding capacity. The 6's can be temperamental, but the close ratios are good. I average about 28-30mpg in my Mazdaspeed, and my personal best was 32mpg. Thats per tank. I drove 57miles one way to work every day, and only 2 miles city each way. So with 4 miles city, 114miles hwy, I had a good opportunity for mileage.
Do you know what rear end ratio you have? The lowest I know of is a 3.90 that is easily available.
You can also remove a ton of weight from a miata, and it is well documented in many sites. I notice you have a great year, the 93, which means you buck the 89-90-91's crank problem, but keep one of the lightest years and smallest engines avail, the 89-93. The 1990's dash is almost 10lbs lighter, so you could swap that in for some savings... Actually, read Keiths article on his car, he did some amazing lightening.
Targa Miata
and there is this fellow too, a very smart man.
Red Beast - Lightweight Miata
the main focus sites for miata's are Miata.net and miataturbo.net, with clubroadster.net being a bit more of a visual mod site.
Anyway, I'm getting carried away, good luck!
Oh, well my project right now is an underpan for my car to improve top end speed, acceleration, and as a bonus, mpg. I would also like autokonexion's kamback style roof, but its much too much money. Good luck! AGAIN!