We have 4 vehicles and only 2 of us can drive. Definitely overkill. Three is the sweet spot imo. Have 2 nice cars and one "beater" car.
For us, the "sweet spot" happens to be 6.
Her mostly reliable, (10 year-old) daily driver small car, and my mostly reliable (15 year-old) daily driver small truck.
I restored an old El Camino and we bring that to car shows during the summer months.
She inherited an MGB convertible from her father and I got it (mostly) drivable so we can at least take it out to A&W a few times every summer. Her dad really wanted her to have that MG, so we hang onto it not only because it's fun to drive around with the top down, but for sentimental reasons as well. Both of the vintage cars have collector's plates, so there's no annual registration costs, and liability insurance for those is around $40 each for 6 months.
We live where it snows for 7 months out of the year, so we have a 22 year-old SUV that has 4-wheel-drive for those rare occasions where we need to get out of the driveway when there's 10 inches of fresh snow, or if we have to help relatives get their vehicle un-stuck. It's also our back-up vehicle most of the year if one of our daily-driver vehicles needs service. It's paid for and runs well, but with good winter tires, it only gets 10-12 mpg, so we only drive it enough to use up a tank of gas each year. It costs $85 a year for registration and $40 every 6 months for liability insurance.
Finally, we bought a new Chevy Trax last year for our "retirement road-trip vehicle". It's new, it's got a lifetime powertrain warranty, and gets over 30 mpg. We only put 2700 miles on it last year, but with retirement looming, we hope to enjoy it more this year and in the future.