There's a difference between modifying a car and "ruining" a car in the way the original post detailed. On one hand, if it's your car, do whatever you want to it! It's yours, and it's there to make you happy. On the other hand, most of the "tuner" cars (WRX, Evo, MS3, etc.) are on their 3rd or 4th owner before the Monster decals and cheap flea market mods get festooned to the poor thing.
When it comes to these cars, especially the turbocharged ones, it's just so easy to make them go a little bit faster than originally intended for next to nothing. Hell, with my first WRX, I dove down that rabbit hole, tuning it with random "known working" maps uploaded by people I've never talked to on a forum I didn't even belong to via a Tactrix cable and my laptop. That's like finding a random box of pizza on a picnic table in a park. Sure, it's a possibly delicious pizza, and it's free, but what's it going to do to you later? Do you have the stones to find out? I did, and it didn't blow the motor into shiny chunks. Others weren't so lucky.
I also learned what to do by following people on forums. Some guy tackled poorly shifting WRX transmissions by making a "cocktail" of random fluids. I did this because other people said it worked. It kinda did, I guess, but I'm sure a good fluid would have done the same thing. I had the STI scoop, the full catless exhaust, the random stranger Stage II tune, the not-so-great Prosport gauges in the ATI clock pod, the grounding kit, all of the Kartboy stuff... it was like a rolling NASIOC forums science project. I loved it at the time.
Now, I sort of knew what I was doing, and I knew what I was getting into and it wasn't my first rodeo. I did a lot of research before diving into some of the mods, but imagine you are a kid today seeing how easy things look, and it's your first car. That 2002 WRX I paid $16k for in 2005 is now $4-5k and has been through the ringer already. You want to make it "cool", so it gets all the crap your 17 year old brain thinks is cool. We were all lame at 17, and you know it!
It makes me sad to see these cars in dilapidated shape more because it makes me feel old than anything else.