Dave, I agree with Jessamyn: Your explanation for using epigraphs as a way of “…letting other voices in” is wonderful.
I also agree with her about overuse and as scaffolding. I have often used them only to omit them on the completed poem or in the completed book. I find I’m using them less and less for the reasons stated above.
I think sometimes we so much want our readers to “get it” that we tell them what the poem is about by using an epigraph, when what we should be doing is trusting our readers’ intelligence and allowing them to bring their own interpretation to the work.
But, yes, as Jessamyn says, we need to use epigraphs “that 1 time in 10 when they utterly change the work.”