Think about some great, documentaries, many do not come anywhere close to having a "broad audience", they just have to be interesting.
Right off the top of my head,here's a few great examples:
Exit through the gift shop-had no idea who Banksy was before and i had zero interest in graffiti art. Saw it anyway, LOVED IT.
Dear Zachary-do not know the family, never even heard of their case, but dear god, how poingient and well made. Their story will stay with me.
Toynbee tiles (i forget theactual name of thisdocumentary, but holy f**k thats a great, weird story)
As viewers, we dont always need to bepersonally touched by something, we just need a great story and a little intrigue. Ray franz`s story has both.