If comparing to the same car with a non-numbers matching drive-train, yes. Whether that is worth $200 or $2,000 is harder to tell, depending on other factors. If comparing to a similar car with a 350 'Chebby in it, a much bigger YES!
I used to be indecisive. Now I'm not sure. I feel like I am diagonally parked in a parallel universe. 1968 400 convertible (Scarlet) 1976 T/A - 455 LE (No Burt) 1976 T/A New baby, starting full restoration. 1968 350 - 4 speed 'vert - 400 clone (the Beast!) 1968 350 convertible - Wife's car now- 400 clone (Aleutian Blue) (Blue Angel) 2008 Durango - DD 2008 GXP - New one from NH is AWESOME! 2017 Durango Citadel - Modern is nice! HEMI is amazing! 1998 Silverado Z71 - Father-daughter project 1968 400 coupe - R/A clone (Blue Pearl) (sold) 1967 326 convertible - Sold 1980 T/A SE Bandit - Sold
In general, yes! for true classic and collectible cars a car with matching numbers always brings in more money. but...with our cars, not unless its a Ram Air, the difference might be marginal. Unfortunately most classic car buyers lack knowledge on how to spot a numbers matching drivertrain and are more interested in first impression and/or restomods. I'd say the split may be 30/70 of buyers that actually value numbers matching. Me, myself would turn away from a non munbers matching bird. But that's me, b/c I've been into Firebirds for 32 years.
I'd say that the 30/70 split is probably a good guess. However as time passes, I believe matching numbers will become less and less relevant except as you noted for the extremely rare unicorns, TAs, Ram Airs, etc. As us old folks fade away, the newer generations will want the looks but not the hassles of originality. This is why restomods have become so popular. So a 400 Firebird with its matching number carburetor will be worth less than a 400 Firebird upgraded to fuel injection. A Firebird with it's original hand cranks will be worth less than one upgraded to power windows, even though they are not original. Just an opinion.