Sensitivity to MSG varies widely. I guess most of us have grown acclimatized to eating MSG, or ajinomoto (especially if one consumes hawker food widely in malaysia). I still personally prefer to stick to natural sources of umami (like the kombu-bonito dashi you talked about, or even ikan bilis stock (iri-dashi!) rather than ajinomoto, though. The latter is processed, concentrated and whilst quite harmless, it does make me very thirsty after consuming it and I do know people with pretty bad reactions to it (eg. vomiting and headaches). I think its like the difference between white, processed sugar and the unrefined sugar products, like gula melaka- its just metabolized differently by the body, subject to personal preference. Thank you for the informative article, Cheesie. I do enjoy reading your writing about Japan.
Full article: http://cheeserland.com/2015/09/the-meaning-of-umami/