Toby makes many excellent points.
The key to fans in most sport is the live experience. People only really watch on TV what they've played or seen in person, even if only once or twice. This is why golf and soccer are so popular on TV, they are among the most widely participated sports in the world.
And it's especially true with drag racing. Once you've seen it (really: heard it), it's difficult to forget and most of us watching on TV are recalling that thunderous live experience. No amount of HD can make your chest pound the way a nitro car can, we're all just remembering what it's like. As Toby and others have pointed out, it's hard to evangelize a 4-second experience unless you've felt it in person.
The key to fan expansion in NHRA, therefore, is the live experience. NHRA needs to aggressively work to get people to the track, especially new people.
I think, IMHO, that starts with dramatically lowering the ticket price. Maybe there is a reserved seat price that's today's $50-$60+ a day for some special fan experience or really good seat, but the bulk of them ought to be $10 or less. Maybe ADRL has it right with free? Get people in the door. They'll buy a hot dog or beer or t-shirt, but get them there. They may turn into a fan for life.
And when you get them there, teach them. Use the interminable downtime to teach people about the sport, not to hold "drag races at the drag races" and toss t-shirts into the crowd. Use the big screens not to show the same ad over and over, but to show well-produced videos that teach everything from what a holeshot is, to what index racing is, to how they tune clutches on nitro cars, to even "how you can get involved in racing". I could come up with a list of 20 three minute videos without breaking a sweat.
NHRA should do more to evangelize participation. Most people I run into at the track think that every one of the 500+ cars at a national event must be owned by a millionaire. When I tell them that I first got involved in racing in the sport with an investment not much greater than a new Honda, people don't believe me. When they find out that most people racing are just regular work-a-day folks who have a passion for the sport and spend the same money on it that many people spend on a boat or on golf, they are amazed. Where are the NHRA videos that say "this could be you!"?
And finally NHRA should stop paying ESPN to get screwed on time slots. As I noted, people will start with the live experience and follow it on TV, not the other way around. People don't turn into lifelong NHRA fans by watching the Little League World Series and just happening to tune into the following NHRA broadcast. People hunt down the sport they want to follow. NHRA should go to Speed or somewhere where they are in fact wanted and get a deal that doesn't require them to pay an ungodly sum to get shafted week in and week out. Save money, get better treatment. Seems like a winner to me.
Just my opinion...
That works out to 168 rounds of competition-42 events. Maybe they dont make enuff? 
