As the toxic quantities are just lower and it can be hard to gauge MSG content in something like chinese takeout, I would really avoid letting your dog eat that... personally.
Question is: when is the amount of MSG added really tiny? If it's that tiny it may either be pointless for your flavor of the food or it's unintentionally an ingredient in an ingredient you cooked with yourself: a trace I guess. (possible example perhaps is yeast extract in some chicken stock that you added to your risotto... It's probably okay in situations like that although the parmesan may be way too salty for your pets too, but it's probably better to avoid things like Chinese with a bunch of ve tsin thrown in.
I won't tell you what to do with your pets but I myself wouldn't use dogs or cats as a "dumpster" (not meant agressively or offensively) with maybe the odd exception when you know what you're giving. I guess leftovers are not during your dnner, but I also have experience with dogs and cats begging at the dinner table, but IMO / IME you need boundaries as not to reinforce that behavior and if you love your pet I think you should not give them your food on a regular basis (i.e. just anything), rather than thinking you are doing them a favor as a treat... The dumpster thing (to avoid wasting food by throwing it away) seems better spent on pigs or goats although there are still limits.
Not that I know much about parenting, but sometimes you gotta say no (just get quality dog food that is nutritionally healthy for dogs if you want to be good to em - at the risk of them getting dependent on it and getting high standards / spoiled).
If you live in the countryside a couple of pigs is pretty cool as a livestock type pet... we used to have 2 pigs at the biological fruit / veg garden I worked at in the past, they lead quite a nice life I believe, and got some veg waste etc... I applied for part of their bio meat when they were getting old and it was time to put an end to their lives. It's a bit weird that I used to know the animals, but it helps that they weren't treated like an object nor suffered.