“Whose American dream? The dream is a chameleon; it has changed again and again. For the first immigrants, America was a continent to explore and exploit, a haven for the unwanted and the dissenters—a new beginning. Gradually the dream became an ascetic and idealized image of democracy, bespeaking the age-old hope for justice and selfgovernance. All too quickly, that dream metamorphosed into an expansionist, materialist, nationalist, and even imperialist vision of wealth and domination—paternalism, Manifest Destiny. Yet even then, there was a competing Transcendentalist vision: excellence, spiritual riches, the unfolding of the latent gifts of the individual.”

This last line references the last line of his DNC speech in 1980 where he said "the work goes on, the cause endures, the hope still lives, and the dream shall never die."
DNC Speech (2008)
Context: There is a new wave of change all around us, and if we set our compass true, we will reach our destination — not merely victory for our Party, but renewal for our nation.
And this November the torch will be passed again to a new generation of Americans, so with Barack Obama and for you and for me, our country will be committed to his cause. The work begins anew. The hope rises again. And the dream lives on.

With the century, vol. 3

Let America Be America Again (1935)

Source: The Awakening

Unknown, but also attributed to Les Brown, a motivational speaker. Commonly attributed to C.S. Lewis, but never with a primary source listed.
Misattributed

Source: Clockwork Prince

Source: Time and Again (1951), Chapter XXXV (p. 183)

Source: Canti