Sadly these valuations are pie in the sky or mine would have been snapped up at 15k. The facts don't support your argument or you could be making a fortune buying them up and selling them on.
Agreed. The 'trade' to 'retail' price differences of £1,500 or so are ludicrous these days. Especially with a 'niche market' car.
A trader will put £4-10k on the purchase price of a car, with no expectation of selling it quickly. If they happen to get the highest figure that will be a huge bonus to them. But they will be happy to drop the price continuously until they sell it; as long as they still have at least £3k profit.
Any car dealer will still tell you they make "£400 a car". That is nonsense. Maybe the salesman is making that but the company won't be.
So your Z3M will be retailed at first at around £18-20k. But they will expect to sell at £15-16k. Anything more than £15k is a plus.
I have seen very, very niche market cars (worth realistically £70k) offered at £125,000 by dealers. HUGE mark up. Purely because there WILL be decent profit in it at some time in the future but they can afford to wait and drop the price significantly.
Personally I think it is partly down to dealers having no real idea what markets are doing at present, so chance their arms and 'test' the market. When your living depends on profit, the 'testing the market' will always start at the highest figure possible.