I just think that the cars should be able to float for a bit before they sink. they also should make splashes. doesn't have to be super realistic though. after cars get submerged electrics don't work? just something random I thought of. splashes.
There does seem to be a little bit of water physics, if you hit the water with some speed you'll see some deformation, though obviously not to the extent that you're talking about. Having the cars float a little bit before they sink is probably way easier than adding splashes, though I doubt either one is a priority.
I think it would have to be at least a little dynamic, otherwise it would look terrible and I'd rather just not have it.