Will MSG improve taste of a food for someone who dislikes the food itself or will it make it worse?
MSG has a flavor itself; it tastes of "umami", the savory, meaty flavor. This is because it's made of glutemic acid (or glutamate), with a little sodium (less than salt). Glutamates are the compounds responsible for the basic umami taste, and they are found in high concentrations in kelp, cheeses, soy sauce, and oyster sauce. 

To the best of my knowledge, it's not like salt, which is said to enhance existing flavors; this would be more like cooking broccoli in bacon grease to impart a bacony flavor to the broccoli. Therefore, it depends heavily on the existing flavor profile of the food in question and the taste preferences of the person involved. If the person likes broccoli dunked in soy sauce, it might be worth a try.