Yup, trade-in values seem like they are never where you think they'll be. It's because we study the Edmunds and KBB values online, and then are shocked by what the dealers will give. A dealer will only pay what the car is doing at Manheim auctions - maybe a bit more or a bit less based on color, rarity, etc. But pretty much what they are doing wholesale is what you're going to get.

If you have any buddies at a car dealership (doesn't have to be BMW, any dealer that has access to the manheim dealer-only website), call them up and ask them to look up what your make/model/year car has been doing at auction lately. THAT is the value you're going to get. And usually, it's rather...um...disappointing