If it is in pristine condition, still make sure it is top running condition, including the oil, tranny fluid, tires, brakes etc. there's no point modding a car unless it's in top shape.
A cold air intake and exhaust will open the engine up to breathe a little better. A note on exhaust; do your homework on piping size, making sure it is not too large (too little backpressure=no scavaging of exhaust from engine) or too small (you just wasted your money entirely). Use only mandrel-bent corners if you're going to bother replacing the piping. Even if the pipe diameter isn't much larger than stock, the stock crush bends at each corner restrict the airflow. Any muffler shop can order mandrel-bent corners. they simply weld them together with stright pipe, like a jigsaw puzzle, custom for your car. This is usually cheaper than an aftermarket bolt-on cat-back system.
Also, make sure to get the larget resonator that will fit your car. this helps cut down on the sound level, without really affecting any gains.
Straight-through mufflers tend to be louder than say, a dual-tip muffler, just FYI.