There's a lot of mis information and bad examples. Here's a counter example:
I have a base SR w/AP
-never had phantom breaking and I drive 140+ miles a day RT.
-The SR and SR+ both have the same sound system. Tesla disconnected the door triangle tweeters, the rear deck speakers, and removed the rear sub. You can add a sub and rewire the other speakers. I did it...and holy **** it was worth the $250 I spent and 8hrs.
-some Sr people have immersive sound, some don't, along with fog lights, ya just roll the dice with that one.
-also...you can call later on to add the SR+ package back to your car it's going to be $4500.