haha tightening things more will make ur car vibrate more weeay, co's car memang got spinning parts, it's unavoidable .. so to prevent these vibrations from propagading to the entire chassis, dey use bushings, mounts, sound deadeners (which sometimes also absorb vibration), foams, anything soft that doesn't compromise too much on the rigidity (sure lar kenot use sponge lol)

even the body chassis and panels are not so rigidly bonded together to allow some twist and flex to reduce the noise when the car is under load e.g. cornering forces

yup, solid stuff is good for the car from performance point of view because it reduces all the unwanted movements between parts. That's why race cars are usually built by stripping off all the heavy stuff (that's another issue), then more welding at various parts of the body or add metal bars and panels to really weak places.

Result? sharper handling, responsive control, driver feels whatever the car goes through

Side effect? farking uncomfortable .. then again, race cars are never meant to be driven on KL roads lol