Hot-rodding cars has been going on virtually since the day they were invented. It's a hobby that many people enjoy. Most people who "hop up" their cars have some experience with car maintenance and repairs, and understand how cars work and how they are made. They understand the mechanical limitations, and accept the fact that any mechanical system is subject to failure.
If anything, the revolution in computerized engine management systems has made Hot-rodding even easier than ever in a lot of ways. The addition of a simple computer chip can result in a considerable increase in power, especially in a turbocharged car like a TDI! Bolt-on kits for suspensions, etc, are readily available and can be installed by anyone with a basic set of wrenches. "No experience necessary," as they say.
The downside is that many people are modifying their cars and achieving big increases in power output who don't actually know very much about engines and drive trains. They may also be performing ill-advised suspension and steering modifications without the technical understanding necessary to keep the car's ride and handling within safe parameters.
The result can be a very disappointed TDI owner. (Or Civic, or Toyota Pickup, or whatever they are tinkering with.) The car goes from being, in their mind, a "great little car" to a "worthless piece of junk" when things start to go wrong.
So before you embark on a program to extract every last drop of power and handling from your beloved TDI, please understand what Hot-rod hobbyists have always known: The more power your engine makes (and especially the more you USE the power) the more prone the car will be to mechanical failures. It's just an unfortunate fact of life. Current Volkswagens are VERY robust little cars, and stand up to modifications and hard driving very well compared to their competition. But when you mess with the power and the suspension, and start driving fast and pushing the limits, you need to know that you'll inevitably break things. The more educated you are when you perform the modifications, and the more carefully you use all the newfound performance, the more reliable your car will be. But regardless of your precautions you need to realize that Hot-rodding is an ONGOING hobby. It doesn't consist of simply bolting on modifications and then enjoying the results forever. Once in a while it also involves repairing the damage the mods have caused to your car! And it requires a different mindset than many people are used to. A fried clutch, for example, will send many inexperienced owners of a relatively new "Hot-rodded" TDI into a frenzy of shouting at Volkswagen and anyone else on whom they can vent their ire. An more experienced performance enthusiast, after the initial disappointment, sees an opportunity and excuse to install a high performance racing clutch. (And maybe a torque-proportioning differential while he's at it! And how about a 6-speed tranny kit? Etc...)
This disclaimer is not meant to incite panic, nor to steer people away from modifications. It's intended to educate, and to warn. Enjoy your car, feel free to play with it, but do so with the understanding that ALL mechanical systems are prone to failure. It's part of the game.
PS. Many different upgrades have been done to vehicles. Some are more "tried and tested" than others. Keep this in mind and weigh it against your risk tolerance before doing any upgrade.
Also remember that what you are reading here on the Internet may not always be correct Some people have ideas and suggestions which may or may not be accurate. Please use your own judgment when taking the advice of others.