I believe that in Nikki Giovanni's poem "Dreams," she is being ironic in speaking about her dreams and society's expectation that black people weren't supposed to have any.
She writes that when she was young, she didn't realize that a black person was not allowed to have dreams. (I detect some sarcasm here, I think...)
Based on what she writes in her poem, Nikki Giovanni wanted to be a singer. She writes of being a raelet, saying "dr o wn d in my young tears," "marjorie hendricks," and "grind all up against the mic and scream..." These are all allusions to the music/entertainment business.
The Raelettes were back-up singers for Ray Charles, and Margie Hendricks was one of the singers in this group.
So for the early years of her life, while she still believed she could dream any dream (when people of all colors and races dream), Giovanni writes that she wanted to be a backup singer for Ray Charles. As she got older, however (and this is where we detect the irony), she figured she would have to settle down and become "sweet inspiration."
The reason I find this ironic is that singing might have been fun, and seemed very important at one time, but when she grew up, she did not really realize she couldn't have dreams. She may have realized that some people weren't about to easily let her pursue her dreams, but maturity changed her, and she "settled" (not likely) for being able to quietly (like the eye of a hurricane...) and sweetly change the world through her poetry.
And so, the message (theme) we find here is that dreams are fine, but as we grow up, sometimes those dreams change into new dreams and become more powerful than we could ever have imagined. She thought she would sing be heard; instead she writes and touches hearts and minds instead—and she is heard in, it would seem, a more meaningful way.
The tone of the poem seems to suggest that this is just fine with her.