Personally, if I didn't have the ordeal I did with BMWSA, I would have kept my 320D and drove it out of plan.
Yes if big items go, especially on the temperamental x35i's, it can be costly, so while you might score, you might not. Its a gamble I suppose.
What I would have done is put the money I was going to spend on extension in a savings account, and serviced/repaired the car at a reputable place, non BMW dealer, like Ross Duncan in Midrand (Garage 808 for the Capetonians).
You will be surprised how much cheaper an independant BMW expert can be compared to the BMW dealerships.
A ex-forum member and friend got a quote from BMW for his clutch replacement of R24 000+. He got the clutch, pressure plate, thrust bearing and a major service done at Ross Duncan for R15 000. That was 2 years ago,that specific car is still running faultlessly.