The value of these rare vehicles are in the hands of the owners, not the buyers, trade or the dealers.
A desperate seller will always take less. There were very few RHD cars made and obviously even fewer on the market. There were long periods of time when there wasn't a single RHD AEROMAX for sale. So when O'Grady's car came on the market at a silly cheap price, that wrongly set a trade valuation.
IMHO this vehicle should never be worth less than 100k ( assuming the car is well looked after - which they all should have been )
I fully understand the limited market these cars have, and of course the acquired taste........ Non the less they are exceptionally desirable and have their place, and as such can demand the full valued premium.
The market always set the price. If a price is cheap there are more buyers than sellers and prices go up. If prices are high and selling is slow then eventually prices will come down.