There are a couple of issues presented in the question that might preclude a full answering of it.  In my mind, the most pressing issue raised is the assumption that Dr. King's speech was meant to depict a social reality.  I think that the power of the speech was that it was saturated with providing a vision of what could be, as opposed to what is.  The notion of most dreams or transformative visions are specifically designed against their social realities.  I don't think that the speech was intended to reflect a social reality.  The mere title of "I Have a Dream" indicates a vision that is meant to be divergent from the existing social realities, ones that preclude the ability to dream, to transform, and to change what is into what can be.  The second premise that might have to revisited is the idea that the dream is speaking of a geographic condition.  While there was a vast difference between the racism and prejudice featured in the Northern urban centers and the Southern conditions, the fundamental commonality was an existence rooted in discrimination, the denial of the opportunity, and the languishing of consciousness being caused by racial prejudice.  In this light, Dr. King's transformative vision was something that could be applicable to either realm, though each geographic narrative was different.

Your question basically address Malcolm X's concerns about Dr. King's strategies and speeches during the Civil Rights era.  Dr. King grew up in the South, but it was in Atlanta, a Southern city that had already begun to make some civil rights advances before other major cities in our nation. So, when he speaks of envisioning a time period when black and white children can play together and the disharmony or jingle-jangle of discord is replaced by harmony, his words would have most certainly come across as idealistic rather than realistic to African-Americans whose experiences prevented them from grasping his vision.  For example, Malcolm X was the grandson of a black women who had been raped by a white man; his father was severely beaten and then laid across railroad tracks by a racist group in Michigan, and Malcolm was told by a white mentor that he should give up his dream of being a lawyer because of his race.  His experiences were not that uncommon for African-Americans during the first half of the 20th century.

So, while I personally agree with Dr. King's "I Have a Dream" speech and believe that it still possesses power today, I can also see how people who had not had the same more positive experiences of Dr. King would view his speech as idealistic and not representative of their own dreams.

From the question, it sounds like you are saying that the "I Have a Dream" speech was out of touch with social realities at the time that it was given.  I suppose that you can make this argument, though I would disagree with it to a large extent.

You can say that this speech is out of touch because it emphasizes the legal segregation that was going on in the South at that time.  You can argue that it ought to talk more about the economic conditions in the ghettoes of the North.

You can argue that King should have talked less about brotherhood and religious imagery and talked more about how angry black people in the North were getting.

But to me this is an unfair criticism because in 1963, the legal segregation was still there.   As long as that was still there I do not think I agree that other things were the "core of racial problems." I think you have to get rid of that first and then move on to economic problems (as King did between the passage of the 1964 Civil Rights Act and his death.