I think that Steinbeck shows that disadvantaged characters still possess the capacity to dream. Steinbeck is able to to show that individuals are able to envision a world of what can be from what is. Despite their own conditions, individuals find a sense of purpose and driving motivation when they are able to envision a world fundamentally different from their disadvantaged condition. Steinbeck does not repudiate this ability to dream, even if disadvantages prevent these dreams from fruition. It becomes the ability to dream and the intrinsic value of dreaming that is its own good, despite an individual's disadvantaged condition.
When George and Lennie travel, it is their dream that enables them to transcend their disadvantages. When Lennie is able to reaffirm the sing- song vision of "I got you and you got me" it reflects how disadvantages can be forgotten, if only for a moment. The fact that George kills Lennie while reminding him of his dream is a reflection of this. Candy is much the same way. His own disadvantaged condition does not prevent him from dreaming a vision of a world in which he can serve his own dream. Even Crooks is able to dream of companionship and camaraderie, while Curley's wife's dreams of being in "pitchers" motivate her being. The disadvantages that these characters face do not prevent them from dreaming. While their dreams do not come true and remain unfulfilled, it is the act of dreaming that Steinbeck believes is part of what it means to be human. In being a disadvantaged human being, one does not surrender the ability to dream and envision what can be from what is.