Great topic.
I do believe appearance matters and
wrote about it. Others have made some good points about vets getting a pass sometimes on appearance but they may have earned that by the quality of their work, but if they sharpened their appearance they would be the complete package.
For people with lesser experience looking sharp my be able to buy you a bit of wiggle room or "political capital" when a coach may want to challenge you. Coaches are predatory animals and if they sense weakness they will go in for the kill. Looking sharp on the field my be able to camouflage other secondary shortcomings on the field. Not to say a coach will grant you too much leeway if you blow one, but you may get the benefit of the doubt.
I think this has to do with the air of authority that comes from a sharp looking umpire who also knows how to use body language and posturing. If you stand upright with your chest out, shoulders back and chin up you look like a much more authoritative figure than someone who is a slouch.