OP sorry to see your damage and understand your feelings. This is a huge problem in our opinion in the Bay area regardless of what kind of vehicle you drive. There are a number of other bay area stories from MS owners on here (including more sad photos of damage). We have a MS and it was vandalized in the same fashion. Our break in happened in San Jose and like you nothing in our cargo area either. When our car was broken into the other vehicle that was vandalized near us was a Honda SUV. We had our dashcam on and they hit ours first and then moved on to the next guy. Our damage cost us $1600 to fix but I'm sure the SUV's was costlier. They smashed and ripped out their whole rear window and also robbed them. We've taken our parcel shelf out, not sure what your arrangement is in the A3. But yes the M3 has similar rear seat drop down access as both of our cars.
A few months ago we attended a Tesla event during Monterey Car Week, and as our car had just been vandalized the weekend before, we brought this situation and costly repair up to Jon McNeill (and believe Franz was there at that time too). Suffice it to say it is something Tesla is aware of. We talked to the guys about more shatterproof window material or locks on the seats as possiblities. When you think about it though thing is if they can't get in one way they will just do it another way. Our service center had several vehicle repairs involving these tiny rear windows in the week we brought ours in and we heard a similar account from another owners who went to a different service center for their repair. We'd at least like to see a redesign of the window/frame area so it doesn't have to be such an expensive repair.
However whether you have a liftgate or a trunk, I don't think it will make much of a difference to the thieves. One MS owner who had his dashcam running got to see the whole attack on his car -- he had the small window broken first, they saw something in the trunk so then tried to break the liftgate window (chipping the glass in it in several places) and when they didn't get an easy break, then went to his passenger side larger window and smashed it open to fish things out of the cargo area since they got the seats down. His repair bill as you can imagine was way above ours. We actually realized we interrupted a trunk break-in in Gilroy when when pulled into a store's parking lot (the guy saw us pulling in and walked away from a car with the trunk left up and what we later believe was a crow bar over his shoulder) so liftgate or trunk I'm not sure really matters. The owner of the car was one of the customer service reps we reported the incident to and she didn't have a fold down rear seat. Trunks are apparently pretty easy to pop. I'm guessing broken glass liftgates are probably more expensive to repair than trunks though.
Ultimately the best way to tackle this problem and those doing it is cracking down on this kind of crime and the perpetrators. I feel it's a means to fund other illegal activity and deserves maybe a bay area wide task force to combat it.
