well there're a lot of aspects to modding. Not eveyone is out to smash the 1/4 mile record or be the next Schumacher.
I'm sure you know those ICE and db freaks. The mods they do mostly concerns the sound. Addig bodykit is just to spruce up the image of the car a bit.
Then some are just out to impress. They just want to mod/customize their car to their liking. and hopefully to judges liking as well.
Last but not least those who are power hungry. Everything they must have some benefits to the car's performance.
Of course, everyone has to start somewhere. So you see a lot of wrongly done cars on the road. Also to quote Joeker, one man's meat might be another's poison.
About JPJ, I guess you have to be very well known to kena like that. But usually ICE people don't kena, because their exterior usually stock. But can blast louder than stadium Bukit Jalil.