So I'm dealing with a very annoying "feature" of hangouts. Namely that while some profile pics show up in my conversation list, they do not show up in the actual conversation. The default headshot icon shows instead. When the conversation has lots of people in it, the picture really helps to identify who wrote what since I don't memorise everyone's phone number.
So if you could take a moment and make sure that your profile pic is a large, hi-res image, that would help.