how about this to an answer to this and the N.E.E.D topic:
a car (any car) is worth a different amount to every single person who considers buying it. Some people wouldn't even consider paying R17k for what, in their opinion, is a crappy old beetle with no power, no safety features and 70 year old technology. In many ways, this the the person who defines the "true value" of the car because he is not influenced by normative factors such as passion, enthusiasm, and other emotions. Instead, he is valuing the car based purely on its quantifiable and measurable attributes. Obviously (because we are on a forum for aircooled enthusiasts!), we are biased in our opinion of these cars because we ARE adding value based on the normative factors above. If you wanted to quantify it, you could come up with a simple formula like so : P = V + X where P is the price, V is the positive(free from emotional and other normative factors) value, and X is the value (to the individual) of the normative factors such as passion, etc (i.e that warm fuzzy feeling you get when you see the car).
This is why we see such variation in the prices of these cars - the seller is basically applying (or taking advantage of in some cases) different values of X in the equation - he is passionate (or knows other people are passionate) about the car he is selling and is adding a amount of money he deems appropriate to the base value of the car (what its "Actually" worth) to account for that passion and enthusiasm.
anyway, my point is mearly that you want to buy cars from people who have very small values of X and sell them to people who have large values of X, all else constant
EDIT: I just thought of another important variable - rarity. If a car is rare, obviously it will attract higher value. I will include that with X though because its not a objective measure of a cars' value. Some cars are downright crap in every quantifiable way, but are worth a lot simply because they are rare, therefore, rarity is a normative value as well, its has nothing to do with the actual value of the car itself (would it still be worth the same amount if there were lots of them?)