I agree with everything about Agnes/Amanda that is posted in this thread, and how her presence sets up various little threads and ideas (Hollywood Blondes, passage of time, etc.).
But I think the biggest thing her scenes set up is how young, inexperienced and naive these girls are. Rose had some degree of real talent to work with June leading the boys (and Louise). But with Louise leading these young ladies, you can tell the act us pretty much washed up. Rose Louise and her Torreadorables would never rival Dainty June and her Farmboys.
BTW I loved Denny Dillon in Dream On, and was so excited to see her Gypsy connection years later.