I think people-to-car scales are okay, the people are "visibly" smaller but big enough to earn the tile they're using. The buildings might stand to be a little bigger, just for the feels. Like an RPG "building" that's big enough to go inside, but not really to scale. ("This impressive castle has two rooms on either side of the hall, and a throne room at the end! So huge!") We're not going inside, so they don't have to be THAT big, but a little more would help, I think.
All the car models in the asset store seem spread between the extremes of hyper-realistic or cubes with wheels. And far too few are "apocalyptic" enough. The Synty "Apocalypse" ones are probably too cube-y for what you want, and I think you can only get them in the big mega-kit.