My degree is in Economics, so I still like to do analysis of markets and business (I am employed as an Area Manager for a large corporation). My take is simple. The gigantic surge in NASCAR attendance and demand in the 90's into the 00's remains a phenomenon. It seemed to be a perfect storm of exposure via TV which brought many more fans into it (especially from outside the south), the excitement fans to brought as they embraced the many characters and heroes remaining in the sport (great cast), and a willingness to spend their disposable income to experience it. Heavy demand drove ticket prices up and made hotel cost skyrocket.
As the costs were escalating rapidly, the advent of large screens and HDTV introduced outstanding racing coverage never seen before. One could watch every single race, with no blackouts. It literally made racing more enjoyable at home, when compared to paying the big bucks to go. This corresponded with the COT, which brought the quality of the product down compared to previous years, AND the recession of 08/09 that hurt employment and wages. The slow spiral downward in attendance started and has not found a floor yet.
NASCAR is not dying, but the business model is not sustainable in its present form. TV and sponsor money drives the profits far more than track revenue, but the tracks must sell seats to keep racing alive. Teams and rules changes will occur, and costs might be decreased, but fans in the stands are necessary to keep the asphalt.