Was it widely seen in, say, Vietnam, as a thinly-veiled excuse for aggressive expansion, or did they prefer the Japanese to their French colonial masters?
Extent dammit.
Believed to a moderate extent in Japan itself, obviously much weaker everywhere else.
Amazingly, one of the major planners of the invasion of China in 1931 genuinely believed in the pan-Asian ideal, but grew to realize that it was a crock of BS as the war dragged on. There's actually a biography about this guy, Ishiwara Kanji, out in English.
One must also question how genuine this concept was when a huge proportion of the propaganda portrayed Japan as "big brother" to other Asian "races" that were painted as something clearly lesser.
Not really sure about Vietnam though.