Coilpacks are pains, generally I think they fail due to the heat they carry from the engine/spark the emit and obviously the spark plug.
I think it'd be a good idea to run the car with the coilpack cover off, lets some heat escape and some passing air help cool them, which i'd imagine would probably help extend their life.
they are a piece of piss to change as well, dealer prices really do take the mickey! I need to start a business up for all the BMW's needing fixed, would make a fortune even charging half of what BMW charge!
Monte Carlo Blue M3 Comp