To be fair bigger cars have terrible depreciation anyway. When I was looking I was tempted by a couple of Omegas, and a 700 series BMW. Their 2nd hand value is terrible. Same goes for most things over the size of a Mondeo/Vectra. What did surprise me is that for the price of a Good 00/01 Vectra with lots of toys I could only get a basic Corsa if I wanted to get something a bit smaller.
The 3 series is much better and holds its value well if you are buying new, otherwise go second hand and about three to five years old. Should still have plenty of life and be a lot cheaper.