As someone who enjoys the costuming part of our sport I try to look like someone of the time. Its not always fancy or over the top but more that if I was in a movie as an extra or in the back ground I wouldn't look out of place. Lots of movies characters have very simple costumes as was pointed out in an above post but when you look at them, it saids "I'm a Cowboy / sheriff / field hand or town folk. They look like they belong in that time. The term "Cowboys" covers a whole bunch of images and time periods when you really think about it. The original post civil war cattle drive cowboys / the 20s and 30s B Western Hollywood Cowboys and the later 50s thru 70s TV Cowboys. Our sport represents all of these and any I might have missed. My personal thought is that when you are at a match you should somehow look like you would if you were in any of these era's.
Like always, my opinion is worth what cha paid.
Best regards,
Chili