FWIW I have already begun spot checking the voltage of our brand new X5 35d at rest, just to get a baseline on how low the voltage goes after sitting over night, etc.

After reading quite a bit about this issue, I'm guessing that it is not usually an 'event' that triggers these failures, but rather a slow decline in the overall health of the electrical system due to:

a - poor charging (weak alternator theory)
b - inadequate capacity (weak battery theory)
c - poor system design (weak engineering theory)
d - the occasional component failure (weak components theory)
e - too high a demand (weak user theory -- favored by dealers)
f - some combination of the above

Note: in all but d (a failed component) the overall health of the electrical system can probably be monitored/judged by its voltage at rest. And more importantly, most of these failures can probably be predicted with nothing more sophisticated than a volt meter.

Funf Dreisig