Numbers matching cars almost always price higher than a similar non-numbers matching cars when talking about original and restored to original cars, could add lightly modified too?
On cars modified with a bunch of aftermarket parts, the numbers matching depends on the buyer. For a restorer, it will cost them money to undo all the modifications, but a gear head will see the performance increase as value so it might be a wash on value?
The numbers matching thing really was hot in the 1990's when prices really exploded on the high end, lower production number cars.
In higher production number cars with /6 or 318 engines the numbers matching was not a big deal.
Think of all the 20-25 year old cars built in 1997 to 2002, and ask if you care if they are numbers matching? Might make a difference on a Viper or Prowler, not so much on a neon or minivan.
So for numbers matching to really matter, you need a low/limited production car (supply) that is wanted by many people (demand).
An example sitting in the garage. Numbers Matching 1969 Coronet 500 with stock original 318 2-bbl, 904 trans, small rear end (not 8-3/4")
Car is getting built 360 with 518 and 8-3/4" rear. Is it worth more or less with the drivetrain swap?
To me it don't matter, not selling the car.