I think you are right Harry the BMW mechanicals are fairly bullet proof the only issues are likely to be those where the technologies meet.
The issue of mileage is a nightmare though. I have 530d 2 years old 70,000 miles worth half what I paid. Been offered one today 700 miles and 4 months old £7k of list.
Anyway Charlie regardless of what you buy on the aero front you'll enjoy it, just make sure its got side exhausts.
