There's a little more to it than that in British English - intonation and position in a sentence relative to other words can change it from limiter as you describe to a positive emphasis. I could say like "Well it was quite amusing" and it'd be definitely a limiter, whereas if I said "That was quite amusing!", would be actually a positive emphasis. If you say "actually" or "really" before quite (i.e. "really quite amusing!") that becomes a fairly strong positive emphasis. And if you put it before "the [object of sentence]" as in "quite the [object of sentence], becomes strong emphasis that is either positive or negative depending on what you're describing, which is I think more similar to the American usage you described. And you can use it just as a term of agreement too - "This is an awful party!" "Quite!" (this usage is bit class and age defined, generally but not exclusively suggesting upper-middle or upper class and likely older).
I think the general rule even in British English is that is emphasizer, and makes things stronger, it's just that in certain situations, it also says "not completely". Isn't English a great language lol?
Australian usage is similar to British, in my experience, don't know about Canadian.