How important is numbers matching?

I figure the more rare and desirable a car is, the more "numbers matching" bs can ad to its value. when you deal with a pro resto shop, you figure they know their stuff and are honest. so much for figuring. they might be chebby guys that think it vin saying it came with a 340 from the factory makes it "number matching" ??? ha
to me the hole numbers thing has long ago run it course except with the big $$$ guys.
I would certainly check the engine to see if it really has been rebuilt. if not, I would call them on the hole deal. just me.