I think if overseas visitors come to the UNITED STATES on their visit, and want to see that Americanest place of pure 50s Americana -- they will go to Disneyland. And while there, I dont think they'll mind an AMERICAN park as long as it is about as loosely themed as DCA's California theme is working now.
I see a small handful of historical/patriotic attractions added to the mix and then ultimately its a theme park competing in 2005's marketplace, so like it or not it will continue to bring in clones of off the shelf attractions that bring in guests.
Until the park is at least as popular as Disney MGM or EPCOT, I think DCA needs to continue building... I don't really see it as good money going after bad, they need to stabilize the park and make it a destination in its own right. Its not even well known in Los Angeles, those who've been mostly have negative opinions of it, and most people only go there as a free twofer ticket or because it's included with the Disneyland passport. Not optional, included. So right now people go there thinking "why not, its free". It's got to be sucking all of Disneyland's profits dry.