I have always extended the warranty (purchased additional coverage/years) on my recent cars. And I will do so with the 6 series too when the time comes (in 2020). Reliable is one thing but none of us are inside there to know what happens or might happen. And as you state these cars can be filled with expensive repairs should something fail. Also if you happen to resell it during the warranty period it will have a bit more value that one without any type of coverage. So I would do that for sure if I was you.
