Do people call them tapes anymore? Anyway, I love audition tapes. I think with active viewing, much can be learned about acting craft and audition skills.
My favorite example is Rose Byrn’s for Get Him to the Greek. In addition to awesome comedic timing, I love the suggestion of the character. We get “hot mess” immediately with nothing more than a few strands out of place and a subtle smudge of eyeliner. She’s not “dressed up” for the role, she’s hinting at it.
However, this isn’t to say that dressing up, when done well, can’t be a successful tactic. Check out Jason Momoa’s Game of Thrones Audition for stellar use of costuming elements in an audition.