Where you are going wrong on this is the false separation of the stereo and the car. Those stereos are not being transported by the car; they have been integrated into it - they are one, car and stereo. The car is also the means of moving the stereo to the location of the crime. Connecting the car to the crime is immediate and integral to the crime. You cannot easily remove a bolted-in speaker system from a car, thus there is no argument that a reasonable person should remove the former from the latter. This is not a stretch of reason by any means, and certainly not the stretch made in the analogies put forth in your counter argument. If the source of the disturbance can be removed from the car without the use of tools then I would agree the car should not be seized.
Furthermore, your private property argument is further shattered once you consider that the car must be on public property (the street) at the time of the offense.
Addressing your "slippery slope" argument, I find it to be a fine argument, and make it quite often myself. Only in this case it's absurd, considering we are well at the bottom of the slope. Your breath is better spent for the decent citizen who lost his right to his home under Kelo than for those who manufacture suffering for everyone within earshot. So before we even discuss whether a local government can legally do this, that point is moot. A principle upheld only when decent citizens who have committed no crime are disadvantaged is a twisted evil achieving exactly the opposite of the intended result.
You should take all that principled passion and put it towards a more noble use than defending the "right" to damage others' ears and disturb others' sleep.
You would make a fine liberal judge...the private property is on a public street therefore it is not private. I am tired of your fallacies and ignoring my points. Go to China. I am done with you.
So? Is any artifact that happens to be used in the commission of a misdemeanor automatically forfeit?
If someone's music is too loud, give them a ticket. If they lose in court and don't pay the ticket, then impound their vehicle. Impounding the vehicle first means that even if the people win in court they're still out the towing and bailment fees (which is, of course, probably the goal). As one opposed to punishing people before they're found guilty, I find this abhorrent.