RP oil is awesome! If you can afford to use it, do it! A CAI will actually slightly lower mileage due to colder, denser air being used. As non-performance oriented as this may sound, go with a short ram or HAI (hot air intake). It'll flow better than factory and the warmer air will give you a bit of a mileage boost. It never hurts to change the plugs, either. I guess it depends on how many miles are on it already. 60k +, change them. Instead of upgrading wires, upgrade your general electrical system. The alternator rewire, S1 voltage booster, and upgraded ground wires will actually help with ignition system (and other electrical systems, too) efficiency and increase fuel mileage, as well.
Another thing: If you can find someone with a tuner, have it tuned. Otherwise, order a PCM from INTENSE or Overkill. I got a tune through INTENSE and, along with better shifting and a slight power increase, saw an increase in fuel mileage as well. At 65 MPH, I can average close to 35 MPG if I try real hard. Normally, however, I get right around 27 MPG doing 80 or so.
