Does adding msg to any recipe or dish always make it taste better? It doesn't seem to have much of a taste on its own. EDIT I'm not asking HOW it makes things taste better, I'm asking which dishes it would work well with, and which dishes it won't. Apologies for the misunderstanding.
As you are no doubt aware, there are 5 basic tastes - salty, sweet, sour, bitter and umami. Umami is the savoury flavour of mushrooms, cheese, cured meats, and so on. MSG is essentially 'pure' umami. In other words, MSG is to umami what salt is to salty and sugar is to sweet. So if you add it to savoury dishes [...] it enhances their savouriness.
MSG improves the savoriness, therefore it can be used in savory dishes in general.
EDIT: For example savory foods are meat, vegetables, mushrooms, cheeses (if not used for sweet dishes / desserts). I think everything which has not a focus on its sweetness [*] or its ... uhm ... neutral-ness [**] can be considered as savory.
You might have a look this this question here on cooking.SE: What is the formal definition of savory?
[*] like fruits served as a dessert, mousse au chocolat, cookies etc. However, I would consider tomatoes, caramelized onions, paprika etc., which might be sweet but not "sugary", as savory.
[**] pancakes, "common" bread (nothing fancy), rice, ...
My short answer would be no.
If you wish to unlock the secrets of MSG, I would recommend tasting it in the raw (go to any Asian mart). To me it reminds me most of instant ramen noodle powder.
The proposition that grilled mushrooms, roasted meat and otherwise hearty flavors taste like MSG is a farce. While MSG plays a role in why those foods taste so good, you cannot take a piece of celery and sprinkle it in MSG and expect it to taste like grilled meat.
There is one category of dishes where actual (powder/crystal) MSG is the more useful choice vs naturally glutamate-rich ingredients: These where you need to keep the water content to a minimum. For example, if one wants to make a fried starch (rice,noodle,...) dish from cooked ingredients that are already on the too-moist side, the last thing one wants to do is add even more water with dashi, soy sauce, fish sauce, tomato paste or other "natural" umami bearers - getting rid of the excess water by reducing tends to have textural side effects that are not always welcome. Nutritional yeast is also not always a good substitute for the same reason (it soaks up water but tends to act as a binder).