Being adaptable doesn't tell you at all whether it is a good decision, or predict whether you should make it. At the limit no decision affects you at all and all decisions are indifferent.
The comparison is between having a single working car that you pay someone to fix when it breaks vs. owning a car that you can fix by yourself by having lots of tools and parts around.
The first is minimalist because it involves less physical material to store and organize. The second is self reliant because you can do for yourself without needing to draw on outside systems as much.
The example you gave is just moving the goal posts completely. The large many car garage case is both less minimalist and less self reliant, so not to the point.
So minimalism is just efficiency? Call it that then.
And frivolity isn't a relevant category to minimalism. You could be minimalist in achieving frivolous ends. Clearly you're carrying too much in the term.