IMHO, dump the 320d, as you'll get bored and the engine is nowhere near as good as a 6 pot. Wait out for a 330d, even one with higher mileage is better than a lower mileage 320d (obviously if looked after).
Speaking from personal experience. (320d straight to 335d)
EDIT: just saw you bought the 320d, great car to start with but i'm sure you're gunna upgrade sooner rather than later!
