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?".
it can't scale to additional layers built on top of it
There is absolutely no substance to this claim.