Contrasts between these stories ought to be a bit more obvious than the above mentioned similarities.
Where one story ends with the dissolution of a friendship, the other ends with a family coming together as a truly unified group for the first time.
Disability is a major element in Steinbeck's story (as characterization and as symbolism). Hansberry's work features figures who are generally very capable (more capable than they are given credit for by society at large), despite their flaws.
One story focuses on class struggles primarily, while the other sees class struggles as part of a racial and cultural struggle happening at the time in the United States.
These are both stories of the dispossessed in America featuring groups that grope after a humble American dream.
In each story the characters largely belong to a class of powerless people, economically and socially lacking power to change their status or situation. This is as true of George and Lennie as it is of Walter and Beneatha.
Seeking positive change and, to some extent, dignity, the characters in these stories express hopes for symbolic and real upward movement. Where George and Lennie begin their story dreaming of property ownership, Walter plays with desires for several modes of ownership but finally takes on the same dream that George and Lennie share.
The symbolism of home ownership is related, if not identical, in these stories. Achieving the ownership of a piece of property demonstrates the notion of self-determination. This specific type of potency and control over one's own fate is a large part of the American Dream as it is commonly understood.