I think you hit the nail on the head. Its really that second opinion before mastering, to say wait up this is wrong... fix that and then we can progress. If its someone to just make it louder, I can do that.
I think it would be good for a couple of times to see what someone with fresh ears and experience can do.
Also, band members know there is something wrong...especially minor stuff, but can't articulate what the issues are. The problem is where its not totally obvious. someone with good ears and experience can say its this or that, or just master it. i hope so that is.