Your original complaint was that your property rights were infringed. Now you're arguing that they should be able to infringe one kind of property right (vehicle ownership) in order to satisfy another (property ownership).
Plus that restriction would be trivial to work around. Just register the vehicle with a friend/parent/PO Box/a registered business/etc.
> That means there are already duplexes with two parking spots that are legal, but I just can't have one if I build it today with more modern, safer building methods.
So your argument for improving your property rights is to take property rights away from other properties that got grandfathered in, potentially evicting people in those duplexes? Isn't that the type of infringement you were arguing against?
> I understand the need for some requirements, like fire safety. That's very important and there are separate rules for that.
There are. But these rules are also for that. The two aren't mutually exclusive.