To address your first post in as few sentences as possible, I can't say I totally agree with it.

I think "assimilation" (it's been a while since I took anthropology, the terms might have changed, and I didn't pass it anyway) should happen naturally, just letting people be people like they have been for centuries.

I agree with Eyeshotfirst, where he says the U.S. seems to have an ambiguous identity, almost a non-identity ( I hope I'm not mis-interpreting your thought).

The "melting pot" thing doesn't seem to have happened at all... Well, at least for the people who aren't fair skinned.