As to the $1 million dollar Alfa., sounds like an austin powers re-run, you are completely right, it sounds like way too much, by 1992 classic car values had crashed to in some cases 20 % of what they were worth in 1990. A lot of cars got wrapped up in insurance scams of one sort or another. It paid to have the car stolen/ destroyed and collect the insurance than to sell it.
Look at Lord Brockett and others.
Secondly, you mention research into German GP cars in the pre war period, what sort of books might have this research, any suggestions ?.