I am quite surprised at how dirty the X3 engine bay gets. Mine is 8 months old, just experienced its first Canadian winter, and the engine bay is full of mud everywhere. Even the underside of the hood has mud splattered on it. My previous car, an Acura TL, never had its engine bay get remotely this dirty.
So in my view, not cleaning it once a year, somehow, in some way, isn't really an option.