You already have a pretty sleek car as it is.

Must likely, even the under body of the car is already pretty optimal.
Newer cars have small spoilers in front of the front and rear tires. You could add them to your car and it would actually 'update' the look.
If you have large open spoke wheels, replacing them with wheels that are less open, and with a shallow lip will help slightly. ( Just imagine that your hand has to brush across the wheel as it is turning at high speed. That is just what the wind has to do, and the smoother the wheel the better )
http://ecomodder.com/forum/showthrea...-6-a-4368.html
Other than that, I don't think you can do much to the car and keep it stock looking.
Do you have a Scanguage ? The ScanGuage would be the single most effective modification that you could make to the car. Since your car is a '93, it might not be compatible though.
Nice car !