Even for you, there could be considerable advantages to hiring an automatic car rather than owning one. You offload the maintenance overhead (though that's smaller for an electric car than an internal-combustion engine); that doesn't save money but it does save time. What would save you money is if your car were off servicing four or five other families during the times you didn't need it. Cutting a $30,000 expense by a factor of 4 or 5 would be a huge cost saving to you. Even if the service imposed an overhead of a factor of 2, it's still not an amount of money you'd give up on lightly.
It need not even reduce your flexibility, if you could summon anybody's car on five minutes' notice. It's easy to see how that could happen, if large fleets were deployed strategically, even in the suburbs. (It would work less well as the density dropped, but even in a residential neighborhood, a car can move a fair distance in five minutes. Your house, your work site, your grocery store, etc. are all likely to be five minutes from a lot.)
There are still advantages to just having your own car. Mine is full of my crap, for example. I haven't taken my toolbox out in a while, but I will, and I don't know when. If I were calling for a car every day I wouldn't lug my toolbox around, and thus wouldn't have it. Customization is nice. Not having to worry about peak usage times would be nice (though peak usage will also coincide with peak traffic, which I try to avoid anyway).
Still... I'd consider ditching a car entirely if it saved me that much money. My car hit 200k miles, and while it's a Honda, I'm still gonna need to fork out $20k within the next few years. (I'm cheap, and don't want a luxurious car. I just want it to get me places.) A two-car household would likely make it very compelling to at least split the difference.