I think about it the same way as owning a boat. If you go fishing every weekend then by all means buy a boat. If you only go once a year for a weekend then just rent a boat. Same principal can be used for longer than 650 km drives
Probably the easiest answer. Not necessarily with the current car rental prices (it immediately adds $300-400 to the cost of a vacation), but overall a decent model.
Not sure why they would get a lot cheaper than they are today. For people who live in a place like NYC, it's pretty common to not own a car and just rent one when they go skiing or whatever. The driving factor tends to be not so much the cost of owning a car but the costs associated with keeping one (parking, etc.) in a place like Manhattan.