How old is the rooster? If you're looking to show, you want to show birds in their first year. That's when they look the best and are in their 'prime'. After their first molt, they have the tendency to loose the high qualities in looks. Take this as an example: My Silver Duckwing Old English Game bantam rooster, Chester. In his first year he was gorgeous. Beautiful tail, nice black chest, and nice white hackles to the saddle. By the time he retired at around age 6, his chest had white speckles through it and his tail wasn't impressive either. The guy just wasn't like he used to be. Now with Chester that's an extreme comparison, but it shows the change that happens after each molt. After the first molt, the bird isn't show quality anymore. If he is, then I'd say you have a prime bird and should definitely include him in all your breeding projects.
As far as diet is concerned.... Diet is huge! What they eat can have a huge effect on the shine, gloss, texture, and more on the feathers. For impressing the judges with a stunning bird feathers, you want to be sure your bird is getting the best high quality food with all the nutrients that it needs. Supplements can be helpful too, as long as you don't overdo anything. My best suggestion is feeding your birds homemade coal. (Not store bought! The wrong coal can be deadly!)