Oh wow, I hope I'm not bringing back a dead thread here, but I have a couple of cents to throw in.
I own and drive a '95 MX-3 with no mods (other than the dents that a couple of deer helped me install). I am getting an average of 37+mpg in combined driving (determined by dividing the miles driven per tank by the number of gallons to refill - maybe not the best method, but consistent over the course of a year). And 40mpg at a steady 60mph with the AC on at full fan speed (done for almost 1,000 miles of interstate one day), and over 40mpg when it cooled down enough I could turn off the AC.
There are a few things that can easily and not so easily be done to improve the mileage of these cars...
Change the 5th gear -
Easiest, but only works when you're in fifth gear
Swap the transmission -
Less easy, but combined with a taller 5th gear would provide what I believe to be the best mileage improvement
Swap engines -
The 1.5L should fit easily (I don't know what wiring changes would need to be made)
The 1.3L also shared a common block (the 1.6L was the largest bore that Mazda would do to the block), but again I have not idea about the wiring changes
There is even a diesel from the Euro and Australian markets that is based on the same block as the 1.6L DOHC that came stock in '94-'95
People on the MX-3.com forum have experimented with rear wheel covers and under body pans, but I don't think they have seen much real world improvement. So it seems that mechanical mods work better than aero mods. I chime in about halfway down this thread
http://ecomodder.com/forum/showthrea...-a-2748-3.html with more info about the transmission swap and 5th gear change.
Altogether, I think that a mild turbo with the cam profile from the 323 GTX (?) which gives 50ft/lb peak more at 2,500 rpm instead of 4,500 rpm coupled with a transmission that has a taller final drive and taller 5th gear would allow this car to achieve over 45mpg (conservative) and maybe even 50+mpg (hopeful). The turbo would not be necessary for FE, but dropping the peak torque down to where it would actually get used would be very nice indeed.