The car-agnostic ideal won't work outside of major cities. The backbone of America is car travel. People outside cities have more space and more stuff. They expect hauling and utility function in their vehicles. This isn't changing.
Maybe if you can convince suburbanites to downsize, you might have a point. But that's also a city-centric viewpoint imposed by limited space and desire to move easily. Neither of those things are desired in the suburbs.
City dwellers don't get it because they don't live that life.
Maybe. Maybe not. The point is to do the exercise for your use case. If it costs you 1.5 hours and rental fees to get a minivan and you need it once a year, that's one side of the scale. On the other side you have purchase, insurance, maintenance, depreciation, storage and fuel costs.
The point is to be honest with both sides of the scale and to actually do the comparison rather than taking an automatic answer "I need to drive extra kids to camp sometimes, so I must own a minivan." Maybe. Maybe not. Just be conscious about the choice, not automatic.
Price difference between smaller car and larger car: $15000
Lifetime of car: 8 years
Frequency the larger car is needed: once per month
Additional time to pick up and drop off rental: 3 hours
Money saved per hour: $52
So it seems that if someone values their time more than ~$50/hour, they should buy the larger vehicle.
Edit: Forgot to take into account the rental fee: $150
Money saved per hour: $2
It looks like it doesn't make sense to rent, as buying would allow the convenience of using the larger vehicle any time, especially if it is more than once a month.
I have a mid-sized car, and I go to Tahoe 3-4 times a year, and probably end up being the driver 2 or 3 of those times. For me, it makes sense to rent a 4WD/AWD SUV with snow tires for those 2 or 3 winter trips, especially since I'll split the cost of the rental among the friends who ride with me.
There's also the comfort/style/happiness factor: I like my car and generally don't like driving big bulky vehicles that are high off the ground; having an SUV as my primary vehicle would make me unhappy.
Sure, anecdotal, not perfectly scientific or even at a good enough scale... but I don't really believe the 10% idea. I'd love to see where their scientific data is on that.
https://www.energy.gov/eere/vehicles/articles/fotw-1040-july...
And I think most people would trade an hour driving for $50.
You can add "additional time to park in the city because you have a big-ass car" to your calculations :)
I doubt those in the suburbs will have any trouble parking. That's a city problem.
Let's say 10,000 miles a year, 30 MPG for small car and 15 MPG for large car, and $3/gallon gas. That give an extra $1000 in gas per year for the large car, or an extra $83 per month if a large car is needed once a month, or $28/hour saved for the inconvenience of the hours spent picking up and dropping off the rental.
Either way, the delta is much smaller than what I was expecting, in the range of a couple of hundred a month at the high end, depending on which way the numbers swing. It can be something that's not worth worrying about, for someone who has a middle class income.
FWIW, 15 MPG would be low for my F150. A Volvo wagon gets 25 MPG, for example. This ain't the 70s :).