My 2 cents:
The cost argument is a valid point and yes you can spend just as much on a IT car as an AS car.
Having been to the Runoff's many,many times and as a 2 time National Champion
Crew chief I know what it costs to win. It takes a lot. Example the 2007 Runoffs: Tire bill was $7500.00 dollars. Now we did win $3000.00 of that back but..... it still had to spent up front. That's a lot but that's what it takes to win.
There are only 2 nationals allowed per track so that cuts down on the number of national events in the division. You must start 4 nationals and be counted as a finisher in 3 as a minumum and can only count your best 6 finishes of which only 2 can be from outside the divison. That's my 2 cents.