Ride height and camera's I choose cars to replace. I don't like body swapping, I absolutely hate it. So If its necessary then ill do it though seeing I use custom physics its really not strange cause the physics make it not like the DB9 anymore. In this case reason I left it on the DB9 is when body swapping on the Cadillac the ride height screws up. I'm not gonna force people to have physics installed just to fix it, otherwise they would also then have to go offline and such. So Its safe to just put it on the DB9 the way it is to avoid any issue's.
As for your "why would anyone replace the DB9 now that we have your SHIFT model for it" You point is alright. Though you have to remember we cannot add new cars to the game so we are stuck to continue replacing current cars in TDU and such others.
I have many Audi R8's replacing the Ascari KZ1 its not like someone is gonna say "We already have a Audi R8 on the KZ1" If that was so then you'd see crap replacements like a Audi R8 V10 on the mclaren F1 or something more stupid.