M3T prices appear to be in free fall, AUC prices for low mileage UP cars went from £100k to £75k in the past 3 months. I'll likely get one when they're 3/4 years old if I can find a well optioned one in an individual colour.
I think all performance cars will go a similar way. My X5M50i insurance has gone up 41% this year and with car tax is now around £730, there will be a lot of people who just cant afford or want to run them anymore.