I would rather replace them
The analogy does not hold. You're not proposing that we "replace" X by X'. Where X is worn off, and X' isn't.
You're proposing instead that we should add a couple extra wheels to the car "because how is that car useful if it can't hold as much people as a bus does?".
The analogy was supposed to be focused on seeing something is going to happen in the future and tackling it now instead of waiting for it to break. Which is where bitcoin is at now.