I figured if I built the whole part, it would help with fitment during assembly too, even if it's not visible when finished. I'm not sure how much will show when looking "down" into the bomb launcher along the chute and I'd hate to leave it blank and have it turn out to be visible from certain angles too.
I hear you about TV shows and movies and how they only build what they need for the shot or scene. I'd use the same philosophy in that situation too. However for my actual models, it's kind of like how I do bang up jobs on mostly invisible cockpits - I never know how much will be seen when it's done, so I do it all. Plus a model is meant to be scrutinized in person whereas in a show it just whizzes by and is gone.
Being as detail obsessed as I am though, I can never fudge things when I have actual references to go by. It was a tough pill not being able to put the rivets on the last part for example. As the saying goes, "time you enjoyed wasting wasn't wasted". My wife just laughs at me. At least she knows where I am!