I feel that "Manhattanization" is simplay a term divised by people who are anti-development. L.A. will never be Manhattan, but I don't mean that in a bad way. Los Angeles will always be Los Angeles, building new skycrapers will not change that.
Yes to outrightly say, "lets give L.A. a Times Square and a Fifth Avenue," is a little ridiculous. Cities should look to foster and build upon a unique individual identity, and not imitate others (and Los Angeles already has a fantastically unique identity.)
But to those who frown on the loss of the multiple-urban-core existence that is L.A., they are worrying for no reason. Unless you downzone the other centers of L.A. (and knock down a lot of tall buildings), you won't lose those other cores, and if you want to preserve them, build them up more as well! (Century City, the Miracle Mile, Santa Monica, Hollywood, etc. aren't going anywhere!)
One could even argue that Long Island City in Queens, downtown Brooklyn, the Financial District, Midtown are "multiple urban cores" of New York City.
As the city grows in population, it needs to grow in density of development. Just because Manhattan was the original dense city, doesn't mean to densify is to "Manhattanize".
