Hmm....apparently nobody is interested in watching Nationwide drivers; shocker.
I realize this is one of those subjects that gets brought up ad nauseum around here, but I don't buy the theory that nobody will watch Nationwide races without Cup drivers for one second. That's actually the kind of thinking I believe got it in such bad shape in the first place. If it was really true, how on earth did it survive beyond the '80s? Or even the '90s for that matter, when a good race could have meant Chuck Bown racing Kenny Wallace or Robert Pressley for a win at Hickory, with V6 engines no less? How could the Busch Series ever have made it with that group of Cup also-rans being front and center? Actually, I think the fact a corporation as prominent as Anheiser-Busch was on as title sponsor for so long tells you all you need to know about what people thought of the primitive, Cup driver lacking Busch Series.
The drivers aren't the issue. If you took all the Cup drivers out of companion events at the big tracks like Texas, sure some folks won't bother going, but I think we're talking about a few thousand, not half the fan base as your argument would suggest. For the most part though, race fans will show up if there is a good race to see. The real problem is that a long time ago, NASCAR began transforming the Busch Series into something it was never supposed to be. They somehow got the false idea that it needed to be a mirror image of the Cup Series to be worth anyone's time. That proved untrue rather quickly. Instead of Hickory and South Boston, they had to be at all the places the Cup cars were. Texas, Michigan, Fontana, and now Indianapolis, that's where they have to be, right? Wrong, but like all problems NASCAR is faced with, they put lipstick on a pig instead of attempting to undo their mistake.
That's my take on the situation of course, but looking at just hard numbers, your argument still doesn't seem to hold water. Stand alone races at Iowa, Road America, and IRP drew 38,000 and 50,000, 36,000 people respectively. That's right on par with what companion races overrun by Cup drivers draw in.
Sticking to Nashville specifically, don't those races typically have their fair share of Cup raiders anyway? How does the removal of those races prove the Cup argument? My guess is that poor attendance there was caused by the same thing that's keeping people away from the cup races at similar tracks. The racing just isn't anything to write home about.