I have just bought a 56 plate with 46k on it and BMW have put a minimum guaranteed value trade in at £9600 after 2 years of ownership, with an average milage of 8k a year. (I got a 2 year warranty free or i wouldn't have bought the car) But BMW put their minimum values low, privately I think I will get about 11-13K for it depending on how many miles i do. BMW give a guaranteed value to give some confidence, but the salesman said they would probably looking to give around 11.5k for 60k 2006 Z4M in two years. But they do BS, but it doesn't sound too far away tbh.
Z3Ms are a completely different ball game they have a massive cult following! I have seen 70-120ks for between 18-25k good ones are 25k+. But i think i will keep my Z4M longer than 2 years, and it will be looked after to the nines. The previous owner of mine was used as a commute so all motorway milage, the car feels like new to drive better than the car I traded in for it. Also I think the Z4Ms will have a cult and are rare following so will keep a good value.
Put this into perspective I have just traded my 320SI, these are really rare only 400 in the UK and only 2500 ever made. Specifically for the WTCC, it has a hand made engine, and is like a smaller M3 loves to rev. I got this 2 years ago for 14k, pretty basic one but most of them were. I payed 14K it had 30k on it expecting to get 10k for it 2 years later. It now has 46.5k and BMW had a book price of £7400 trade. I was furious, but managed to up the value to £8500 trade which still is pretty awful, but the market is rubbish. Especially as it is only a 2.0 4 cylinder and is rated at 30.1mpg but really I have averaged about 26mpg out of it. So may just be the more thirsty car market or this car is a very specific market, hard to sell compared to a normal 320i of the same year they do 45+ mpg. I bought the car because I like cars know one else has, this is why i love the Z4ms and the z4 coupes because you never see them!
Also you expect to loose money on cars it is a mugs game, but in my opinion its life's little perk, and I would do it every time. The values aren't to bad really the money we are talking about is relatively small, think of the poor guys that spend £65k on a brand new M3 and then 3 year later they get a trade in price for £27k. My dad being that person, imagine his face... ye it was purple! but at the end of the day if you can't afford the depreciation don't buy the car, if you want to make money buy property not cars... they are all designed for product obsolescence unless you buy a car and never enjoy it and it sits, so it is always mint and you have 50 years to spare.. The enjoyment is what you spend the money on! SO DO IT!!
Tom Scott