Even though the basic nitro car is awesome, you can add some things to make it even better!
The first thing you can do is swap out some of the plastic parts for more durable aluminum. It costs a bit more, but it keeps the car from breaking in some spots if you wreck bad. I'm not sure about other companies, but the NitroRCX website sells tons of aluminum upgrades. They are totally optional and the car will be perfectly fine if you don't want them
The next thing you can do is waterproof it. If you drive an unmodified RC car through the water, the servos could get damaged, and they cost $25 each. To combat this problem, simply put large balloons around the servos, and zip tie the opening shut. I am not going into detail about the process, but if you SEARCH it, you will find how to do it in detail. I highly recommend doing this even if you don't plan to drive through water directly.
Another thing you can do is add LED lights to the car. A good website that sells lights specifically for RC cars is RCLightHouse. You can add headlights and brake lights, ect. The buggies don't really have good spots for lights, but cars and trucks do. The lights make it look awesome at night.