How does observing another audience (Theseus, Hippolyta, lovers) help understand the relationship between audience and performers (rude mechanicals)?
We become the the audience for the drama played out by Theseus, Hippolyta and the others. These performers, in turn, form the audience for the reenactment of Pyramus and Thisbe. How doe observing another audience help understand the relationship between audience and performers?
When you observe a play, you may or may not understand how well the characters know one another through the script alone. When they listen or comment (unbenownst to the other performers), you might learn subtle insights into the true feelings of certain characters as opposed to the feelings they express openly to the same characters. If there is an undertone of strife or hypocrisy, you can gain understanding through the reactions of characters who are listening in on other characters.
I am not certain if this answers the question you intended. Hope it helps!