"You cannot in all honesty compare the racing modifications of back then to the completely custom-built dedicated race cars they run today."
Of course you can't, but my point is still valid. Cars that have come stock from the factory have been modified since the beginning of NASCAR. NOBODY ever ran a car stock from the factory. The fact that with each passing decade the cars are modified more and more does not detract from that. Today's NASCAR race cars are NOT modified for racing at the factory. They are bought stock, and THEN modified.
If you've got a problem with the top NASCAR racing series, such as the Busch and Nextel cups, in which the cars are very heavily modified, then look to the lower levels, that is, the 1/2 to 1 mile asphalt track racing and the dirt track racing, where the cars come stock from the factory and are much less modified.
The fact is, hardly anyone wants to race a car that is completely stock. Stock car racing is largely about racing a car that you've modified. And hardly anyone wants to watch races in which the cars are completely stock. Deal with it. Or admit that you just aren't into stock car racing.