Much? No not really, but kind of. From the stock setup just some basic changes such as ride height, droop, camber, shock oil (stock is too light) and roll bars. Just for personal preference or fine tuning for myself.
One of the big changes that really effects the car is reducing the amount of rear toe and how much toe is added under compression, this seems to free the car up.
Another change that I did, and I'm not totally sure if it was beneficial or not was in the rear of the car. I run the front upper arm (SER401823) in the rear of the car for two reasons, first it keeps the parts count down and secondly, the front arm is slightly longer, so it provides more material for the ball stud to thread into, makes it a little more bullet proof.
Now, on my car I also did another change in the back of the car, and you may have seen this mentioned by others as well. I take the lower rear arm and trim the nub that the ball stud threads into and shaved it back so that the profile of the arm is flush across the entire arm. Then I use the front steering hub from the X20 (which I believe the 4X also used)(SER401810), and use it in place of the original rear upright. This will change the rear axel location slightly from what the stock setup is like. It should free the back of the car up a little more. There are a few racers that do this but they actually run the front lower arm in the rear as well, but this changes the lower shock mount location so a different shock tower is required as well. Felix Law suggested the method that I use, so really you only need to get a set of front steering hubs from a X20 and you'll be set to go. The only thing you have to remember if you run this setup is that your track width settings are done using the front measurements in the rear as well. Now is it beneficial? I can't really tell but it hasn't hurt the car, maybe on a bigger track it will show up more.
Another option that I have started to play around with is the brass arm weights(SER401962), they make the car feel numb, but in a good way, not sure how to really explain it, but something worth checking out. The only thing when you run the brass arm weights is you have to flip the ball links (SER401807) for the roll bars over as there is no way to get at the grub screw. I drilled the top arms with a hole just big enough for the hex wrench to pass threw to access this from the top and it works very well.
Other things that I changed but probably didn't have to, are the shock bladders, I use the SER401832 as I get a better build out of the shock when I use these. I also change the diff seal to SER401784, as I find it just seals the diff better. Speaking of diffs, I have seen a few diff failures, so I tend to r&r my diff about every 5 race days, just to be sure. I haven't had the gear failures but I change the oil out on a regular basis.

Hope that helps, and if you have any other questions, please feel free to ask.

Thanks
Gary Lanzer