Uh, slot cars and shooting (target) ARE competitive events. That's the point! I think most people build audio systems to actually listen to music. This is mostly a solitary event, or sometimes shared with a close significant other. I'll even go as far as some folks get together with other interested hobbiest to enjoy listening together. However, I don't think listening to music is a competitive event.
In general, I don't think most of the people that frequent this board have much in common with the people that do car stereo competitions. That event is about LOUD and breaking things is common and a sign of success (windshields). Here, breaking something is generally a bad thing!
If you get into home audio in an effort to try to one-up your buddy, you are going to spend a lot of money! Oh, and you will likely miss the whole point of the exercise!
Enjoy,
TIC