the DDP does give you more cameras, and that was confirmed by my SA too. maybe i'm in the minority here, but i just think the blind spot display is such a widespread feature in other cars that it shouldn't be locked behind this upgrade at this price (9k) and of this car caliber.
in a way, i think they were smart locking the massage chair behind the GT, because it really forced buyers to pay a "premium" with that jump. i just think that premium jump was too big to justify, and may have cost some reservation holders like me. if it was $20k or less, i think i would have done the jump...~$28k for massage chair, 100 miles more range (which has diminishing returns since this car already has crazy range), and more HP. i know there are a few more subtle differences, but those were probably the three biggest selling point differences.
but in general, i think you're right, at least with this 9k, 1) it's not as expensive as tesla 2) we're getting actual tangible upgrades, physical (lidar and more cameras) and software (360 and blind spot display)