If you had a model with an m54 motor I would be inclined to say it could be disa/ccv/4 hoses of the apocalypse related...but you don't....and if you did usually a MIL happens. You have an n52 like me...not the same problems.
Battery would have been my first thought too...the only thing that comes to mind is 1 question:
1) your wife's terrain issues (that is a bummer) leads me to think you might live in a wildlife area with rodents that might chew wires. Have you checked your main power line to battery from the starter/alternator to make sure nothing has chewed into it?
Outside of that I don't have a thought. You have new plugs... Ignition coils should be fine...hmmmm