I agree with everyone so far which makes it tough... Well except for the "give it to Nick" option...
I wouldnt change how it looks at all. I mean other then it may sit a hair lower but nothing else. The improvements would be purely to correct some issues with the car.
The front struts are shot... It bounces LOL. The cars are VERY weak between the front subframe and rear frame rails, subframe connectors make a HUGE difference in 3rd gens. The the stainless lines and pads just for safety. And the gears bc the thing has 2.73 in it and is a DOG off the line and accelerating which is all you really need for auto-x. It's not a "speed" race. It's all acceleration, braking and handling. The IROCs came with beefy sways and are actually pretty good performers with minor changes.