I hate to oversimplify things, because just as soon as I think I have a pretty good understanding of something, someone brings up a different point of view that I hadn't considered, and I could be completely wrong, but...
...I think Wes hit the nail pretty much right on the head. Our sport is simply not as spectator friendly, as most any race held on an oval or 1/4 mile. If a person can't see the whole race at the same time, and even then be able to easily make out who the leader is, they lose interest pretty quickly. I honestly think it's as simple as that.
My personal experiences validate that premise unfortunately, to me anyway. I usually attend one NASCAR race a year, and there are times in the middle of the race where the leaders are deep in lapped traffic, and it's difficult to follow the action. Even at Bristol, a half mile high bank track surrounded by 160,000 people, I have fallen asleep in the grandstands in the middle part of the race when it becomes difficult to tell who is racing who. It's possible that I have an exceptional case of short attention span, coupled with contributing factors like 24 oz tasty beverages, that precipitate this condition, but I think most people will admit to losing interest in any competitive activity when they can't tell who the probable "winners" are. In our case, where there are multiple classes racing at once, and even within those classes there are many different types of cars, and then one can't see the majority of the circuit, it's basically impossible to follow the action.
I'm sure there are many on this forum that find roundy-round to be boring to the point of inducing narcolepsy (if not downright annoying) for various reasons despite being painfully aware of it's existence. We have to allow and admit that the same basic perspective is possible with regards to road racing. Sometimes when a person loves something, they can't understand why someone else doesn't. That's possibly part of the quandary.
If one looks at spectator count apples to apples, it's plainly obvious that road racing never has had the numbers that oval racing has. It's not a judgement, it's just a reality, with a few possible anomalous examples like F1 and the Indy 500. I think these have the audience they have because of the carefully constructed format and status as the pinnacle of their particular type of racing, in this case open wheel racing.
There is a saying that goes, "In oval racing, the fans know the names of all the drivers, in road racing, the drivers know the names of all the fans"... the insinuation being that road racing drivers know the names of the fans because they're mostly their own crew or family members. Spectators are defined as people that don't have any direct connection to the drivers. Phrases like this don't find their genesis and get a foot hold into common vernacular without a situation being wide-reaching and persistent.
In my tiny world, this theme has proven to be correct. I started out racing on ovals, and there were always a notable quantity of spectators. At Monroe, 7-8000 people would regularly show up for Saturday night races. The very tangible upside to this situation was that race entry fees were low, at the time $50 for the whole day, and if you took the green flag you got $100. It didn't matter if you finished a lap, you still got the payout and 25th place points if there were 25 cars starting the race, but that's another discussion for later. If you were lucky and good enough to win, the prize was $1500 cash, not that I ever came close enough to know what that felt like.
Unfortunately, even the spectator counts at these types of events are falling. I don't know what the driving forces are behind this, but I suspect it has something to do with the evolution of technology where people's instant gratification needs are being met with ever greater efficiency in the form of 4G networks, Blackberrys, etc.., and real world experiences are being replaced by convenient simulations.
That's a tangential and philosophical discussion that could easily spin off the original subject, so I'll just close with my thanks to those of you that are considering this matter in the best interests of Conference.