The market is always an interesting discussion. Yes, these cars would be a lot more affordable were collectors not involved, but they are. The upshot of that is that were they
not so valuable, about 80% of the parts needed to restore them wouldn't be available. Let's be honest, if a '68 Charger or '71 Cuda was a max $20K car, nobody would've bothered stamping out sheetmetal or reproducing all the little parts that are available. There's a good reason nobody's reproducing '79 Fiesta fenders.
The Gibb Nova appears to be the closest thing to a Hemi Dart Chevrolet had, but that doesn't mean it commands Hemi A-body prices. Non-Mopar people know of the Hemi A-bodies, but few have heard of a COPO L78 automatic Nova. The SS Hemi cars were flat-out race cars, where this is nothing special other than an otherwise-unavailable automatic transmission in a standard production car. No lightweight parts, nothing stripped out, no ridiculous engine. I would bet 95% of enthusiasts would prefer the 4-speed version available at
any Chevy dealership at the time. Rare doesn't always mean desirable--ask a '68-'70 Slant-Six Charger owner.
It appears this particular Nova sale is from a private seller. Regardless, dealer or not, the
market determines the price and whether the car sells. I'm sure I've posted
this tragedy in the past. It's literally been for sale for years. Several standard auction-format sales have been attempted; bidding never reached $30,000. That's nearly six figures less than the current asking and the original classified ad was for $150K.
It would be interesting to see how close to the number this car gets, but despite its proximity (a short drive up the road) I don't care enough to stay after it.