Yes and no. A well-kept and maintained instrument says that its owner cares about the music and the instrument, so is likely to play well - or as well as their ability allows.

A battered, bent and bruised instrument, on the other hand, can send the message that its owner doesn't care about looking after what can be an expensive investment......and if they don't care about their instrument, what else don't they care about? Playing well? Annoying or boring an audience with a crap performance?

Even ukuleles. I have two hand-made ukes which play beautifully (even for a mug like me) and look gorgeous, even though they don't dazzle with sequins and glitter.