New battery costs ~$350. Okay, you might be able to change your own oil but what about the other stuff?
I didn't think the expected value calculation of extended warranty is worth it. Obviously each person will have to decide this for themselves.
For some, local shops are not an option. Unless you're in a big city, relatively few shops work on BMWs. Of the ones around here that do, I'll use them for small stuff like an oil change but don't trust them for major repairs like the overheating issue. Plus, they don't always cost less. One place quoted me $560 to replace a sqeaky fan motor (climate control) or whatever it's called, dealership said it'd cost $380.