Unfortunately, styles change all too quickly in our country, and I think especially quickly in Los Angeles. Thus they felt the International Style out of date in the 1980's and updated the LA County Museum with the new Postmodern style, which now looks bulky, ugly, and dated.
I think 50 years is usually the dangerous time. When a work of architecture is about 50 years old, it is apt to be too dated and in danger of being torn down. But if one would wait another 50 years, it would have been heralded as a fine antique of its era.
In Europe, works are not old until they are closer to 500 years old, and there is less random tearing down and rebuilding according to temporary fashion.
I should probably visit the LA County Museum of Art before pronouncing such qualities as ugly, etc. I don't know when I'll next get to the Left Coast, however.
Ironically, the LACMA bought the old May Co. building a block away for expansion space. It is a wonderful Art Deco style building of '30s vintage, and has been restored.