Agreed. There is a limit but you can't dismiss the upgrade option as infeasible.
Even on your standard car seats can usually be swapped out in under an hour (Four bolts per seat, disconnect one power cable - Reverse to reinstall) carpet + seats takes longer but still only a 3-4 hour job when I've done it in the past. Usually dealers will charge an insane markup replacement parts though "bundling" them into an upgrade package (for less then the sum of purchasing individually) seems to make sense.
As someone who only wears Allen Edmonds shoes, there is a limit to recrafting. I have a pair of shoes that I absolutely love, and they have been rebuilt once. But I fear that the insoles are quickly approaching the point of no return, such that Allen Edmonds won't/can't rebuild them.
Everything can be rebuilt, but there is a point of depreciating returns with things like car interiors.