Nascar is a victim of its own stupidity. Arcane rules...........
Things like the segment cautions really don't help NASCAR much. But it does keep the cars in a closer pack. We all like close racing.
The first thing that started the downfall was when NASCAR abandoned it's fan base in the south east, built cookie cutter tracks in places where there were few REAL race fans and robbed dates from great traditional tracks.
Next came the Toyota....... What a sham. ALL about the money. Dodge, the most performance oriented American car, is not even in the running. Somebody dropped the ball there.
As for the cars being so generic, one word. SAFETY! If all the cars are constructed the same then all drivers are equally safe. I, for one, never like to see anyone get hurt. I have friends out there.
Another factor for the spec car is controlling cost. A single sponsor team just can't compete against the big, multi car, multi sponsor teams. Example...... Kurt Bush with team Denver Furniture, A single car team, can now run with the best of the Hendrick teams. A level playing field will maintain a full race field.
There are many facets to the sport of racing. There's the racers, the race fans, and the business/industry. NASCAR is still struggling but the recent Darlington race, (one of the two best tracks IMHO), was a sellout. That hasen't happened in a long time.