If there's music in the movie, it had better be good otherwise it can bring down the whole thing. BUT a bad film can't be enhanced by good music. If the music is good it will stand on its own merits, but the film can still be rubbish. Just my thoughts
Music can enhance a mediocre movie, in the sense that it can be used to change mood, create tension, or focus attention to the plot. The best music in a movie is the kind you don't notice. It is subtle and becomes a part of the plot.
About 75% of the original Land Before Time's power is in the music. It is wonderfully animated, but in terms of plot its incredibly thin (after having re-watched it as an adult). It absolutely enhanced a movie that would have otherwise been anywhere from alright to pretty good.