I wonder if tossing a couple pillows into the rear of the Y would absorb some of the "boominess and pressure". Interesting that Model X doesn't seem to have that problem, even with a larger "boom" box. I would think that, as all cars have ventilation to the outside at the rear of the car, the car would not boom. Maybe you have something blocking the rear vent outlet?
I personally would not pay for "applecarplay", so I'm glad they don't charge me for it, presuming everyone wants it. As for blind spot notification, I use a wide angle blind spot mirror stuck to the area of my mirror that reflects my car. Wanting notification seems like you'd want that for any cars reflected in your mirror, whereas I just look over and see who's coming and who's there. And you need 360 degree view to park? You must do a lot of parking. Or maybe you don't, seeing you think you need help. Like training wheels on a first bike, maybe.
I think you ought to buy the e-Tron. I wave at all e-Trons when I pass them. Personally, driving the S, I would say Tesla is a Luxury Brand. To each their own.