What value should I put on my Porsche 944 Turbo?

I own a Porsche 944 Turbo 1987. I have owned it since 1990 and it only has one previous owner with a mileage of 91,000. It failed its MoT for the first time this summer due to rust where the sills join...

Why have prices of the MGF plummeted?

The most spectacular crash in any car's value in recent years has to be the MGF. Please give me any reasons that would explain this phenomenon. Are they good value for the money?