"I'd like to see the movie the composer thought he was scoring."

Had the original movie director been given more time I think he could have had a watchable movie without MiSTing. The elements for a heartwarming movie were there, they just needed a couple of rewrites to polish them up.

Why did the cars in the parking lot blow up so easily? Were they powered by nitroglycerin?

Presumably the same reason any movie car goes up in an impressive fireball if it gets nudged. The auto industry of the fictional reality in which movies exist use explodium as a standard construction material because it allows the vehicles to pass the California fuel efficiency requirements.

To Quote Teal'c from SG-1, "Why must everything in this script inevitably explode?" ;-)

Can you say E.T. knock-off?