The loud systems usually do not bother me, only in two cases. One, the bass is so jacked that it causes the car to rattle. If you are going to put money into a car do it right. Two, the people in the car go into a store but leave the stereo turned up. If you are not in the car what is the point of letting it play?
I have done a little upgrades to my car, nothing major since its just for my enjoyment not any shows. Did not want to go for something loud and thumping which made the music sound horrible. Upgraded to a Pioneer Avic head unit, component speakers in the front, coax in the rear doors, 12in sub in the back, with separate amps for the speakers/sub, and a capacitor on the sub. For my little Scion xB RS7 it does its job just fine.