As an anecdote about any amount of parking winds up being used if it's free: there's a guy a block over from where I live in dense, transit-connected Brooklyn who has, at any given moment, at least 6 cars parked on the street, that he tinkers with and seems to occasionally buy and sell. The houses on that block sell for around $3-4 million these days, but the parking is free.

The neighborhood is also quite clearly full of cars that basically never get used—given there's no cost to store them, the owners save them for an occasional trip and in the meantime they accumulate snow/leaves/pollen etc the rest of the year, in proportion to how long they sit without being used.

The dysfunction of this system is particularly aggravating when you have an actual need to park nearby your home, e.g. if you're loading/unloading heavy things, and there's never any space. I would love if every block had temporary loading zones, but people freak out about the idea because it requires taking away some free parking.