Imagination plays a rather large role in Tennessee Williams' play "A Streetcar Named Desire." Perhaps the most poignant part where imagination is apparent is through the character of Blanche.
Blanche is a woman who is caught up in her own illusions. Essentially, Blanche's world is a complete fabrication. She alludes to her age, her past, and her intentions. Blanche is not willing to accept that she is aging--shown by her covering of lights with her paper lanterns. She even tells Mitch that she is younger than Stella (when in reality, she is around five years older).
Secondly, Blanche's past as a prostitute is covered up by her stating that the men from her past are going to save her and give her the life she expects. In the end, Blanche's illusions compound at the end of the play (by honestly believing that Shep is coming to get her and take her on a cruise).
In the end, Blanche's illusions (or her imagination) eventually takes over her reality. Therefore, the impact and importance of imagination in the play is used to lead Blanche down her path to destruction in the same way Desire brought her to Elysian Fields.