Personally, I don't believe my life is quite worth the money I'd have saved by driving a small sedan instead of the larger vehicle I drive.
(If it were, then I daresay my budget would be severely lopsided. Seriously; what kind of idiot would I have to be to spend more than 70% of my net income to car-related expenses?)
The semi-worst-case planning delusion is why we have convoys of 2.5 tonne SUVs doing the school run with two kids each. There doesn't seem to be any way to end the constant vehicle size escalation other than through legislation.
SUVs are at the upper limit of what most people are willing to tolerate in terms of unmaneuverability. Too big a vehicle, and you have trouble passing and weaving through the shitty commute traffic.
And if you try, and the vehicle is too slow for what you're doing, you'll probably crash. So it's a balance between being more survivable and being less likely to crash in the first place.
Also, bigger vehicles tend to be more expensive, non-size-related factors held equal.
This reasoning reminds me of the tragedy of the commons.
You bet I need some fancy footwork to avoid being forcibly detoured. And you bet that once I'm in the correct lane, I make a point of emulating the people far in front of me, by almost-tailgating the person directly in front of me.