The transportation that somebody uses will often reflect their socio-economic status to some point. That can be useful information. However, transportation cannot be enough by itself to give a complete picture. You might have a guy living in an amazing home with a huge savings account taking the bus to work because he doesn't believe in spending money on a depreciating asset, while the guy in the BMW is about to have it repossesed and get kicked out of his home.

Cars are a big investment so I think personality has a little to do with choice of a vehicle.

Just because they bought a nice car doesn't mean they actually have the money to keep it.  Or if they're on the bus, sure, chances are they're not high income earners . . . either that, or their car broke down.