Just remove a part out of the engine bay that is critical to start the engine? Is a car theif really going to be carrying around a set of injectors, spark plugs, a battery, or a spare fuel pump?:)
Really, if they want it (and are professional), they will somehow roll it out onto the street and flatbed it away.
Best thing to stop that is a motion sensor rigged up to a very loud alarm. (Although would suck if somebody bumped into your car).