My annual maintenance costs + insurance + licensing on my 15 year old car are about the same cost as renting a car for two days.
I think you vastly overestimate the cost of owning an older car.
Im also not sure you understand the term flexibility in the way most people do. Right now (as in within 10 minutes), I can be on my way up to Lake Tahoe or off to Yosemite. There is no other form of transportation that can work that quickly. Even with an amazing rail and bus network, you are beholden to the schedule and the overhead of local transit to the long distance station. With public transportation your life is dictated by the schedule of the transit, with a car you just leave whenever you feel like it.