I'm world's away from you on this.
You mentioned '50s America being a great era of American fashion, which seemed odd to me given so many designer's obsession with the decadent American '20s and it's oft-emulated haute couture. I think that the '50s was really the beginning of the American consumer's commodity fetishism, which has indeed become a global phenomenon over the last several decades. The '50s had a very profound and prolonged effect on the American psyche, everyone after that American dream (the 'image of perfection' without basis in reality).
I'm not a fan of globalization and I see the outgrowth of the capitalist fashion industry as having as pronounced a negative effect on the global citizenry as it has on the American citizenry. Fashion as an art form really only means something to me when it is detached from the realm of commerce and mass market appeal, I don't even wear anything that isn't. The commercial fashion industry has become an image obsessed ideological institution that's package is delivered to the consumer with a lingering neurotic self-hate. We couldn't all be John Waynes in the '50s and we certainly can't all be [popular male icon]s now. But there's a social pressure to be up to par, to be both completely image-conscious and image-perfect ourselves. The only choice a sane, rational human being that can't fit the mold has left is to abandon all of this. However, sanity is a fading afterthought in the collective memory of America, so the choice is typically made to become a member of the delusional self-loathing class of citizens, the American bourgeois.
Art suffers at the hands of the corporations today just like art suffered at the hands of the catholic church during the renaissance. Powerful interests will invest money into the art, but at a steep price: the sanctity of human expression.