I put a short ram air on it and am consistently getting 40 mpg in San Jose CA The lowest speed limits here are 40 though so I mostly use 4th or 5th gear. I bought it with 235k on it and have put 30k in the last 2 years driving over a windy mountain highway every day. (highway 17 if you know it.)
Gas mileage and reliability. This thing is built like a tank. I am constantly revving it up to 6000rpm and it hasn't complained once. I will be buying a 2001 GT-S in the next couple weeks and I just needed to do one last thing for my car.
Short ram intake. You will notice a BIG difference in your low end torque and smoother power through the rpm range.