In The Glass Menagaerie, what is the significance when Tom breaks the fourth wall and talks to audience directly about seeking adventure?Scene 5

I think that there are a couple of reasons that Tom speaks
to the audience.  On one level, it is almost as if Tom is pleading with the audience for
absolution in terms of abandoning the family.  Tom seeks the adventure and the
excitement that he perceives is not a part of his current life.  Essentially, he seeks a
life that is different from the one he leads.  Understanding that there is a level of
abandonment involved in this pursuit, Tom is quite content with being "a bastard son of
a bastard" and leaving the family to discover this "excitement" that lives in a world
outside of his own.  Yet, there is some level of guilt involved with such a move.  His
speaking to the audience is a hopeful way of assuaging this guilt, trying to explain it
away and breaking the wall between character and audience is a way to achieve this. 
Williams is a writer who explores the level of cruelty that family members display to
one another.  We see this in other plays, such as sisters betraying others' trust, or
sons and fathers not being able to connect.  In Tom's case, he is going to leave his
family and in abandoning them, he speaks to the audience as a way to explain what he is
going to do.  For those who break these bonds, Williams might be asserting that there is
some external force to whom they plead in order for understanding behind their actions. 
It is in this vein that Tom speaks to the audience.