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.