The Z on BJ's auction was a 1974 260z, not a Series 1 240z. That is a huge difference in the collectible market. Pristine, low mileage, low vin show room early Series 1 240z's can go for over $50,000; if a Series 1 they can fetch over $30,000.
http://www.classiczcars.com/forums/showthread.php?t=31271&highlight=50,000