I think sanding may help if you have a lacquered Brass - it will take off the worn lacquer. Otherwise I wouldn't see a need and would be concerned I'd scratch the brass or the surrounding leather.
I just polished up brass connectors on a Dooney with my trusty Simichrome polish and they came out fantastic! (I have the SimiChrome forwhen I'm rehabbing pencil sharpeners - but I digress) my other favorite metal polish is Nevr-Dull, which is a fiber wadding (cotton?) that has been impregnated with polish. Both are readily available on
Amazon.