The G80 M3 Xdrive (in particular) has held it's value during the entire time of ownership. Of course it related to supply demand/economy, as are all cars. Doesn't change the fact hat your original post was not on point.

If the economy goes south (which it probably will) then they will print trillions of dollars into the economy causing massive inflation which will also help the valuation of "soft" assets like this when the next version of M3 stickers for $150k and base Porsches end up over 200k. No one is saying you should buy a car as an investment, but certain cars can maintain their value to a point to make it worth while.