You have to look neat and presentable. I would go with the shirt, tie and slacks, maybe with a ?sports? jacket... You need to present yourself as proud and confident. Confidence relies on how you are dressed. Are you comfortable in a suit? Will a suit make you nervous? How professional is the environment? A small theatre, in a bogan town you could walk in wearing a dressing gown and moccasin boots and get the job, for a large, in-demand job in a professionaly environment, it may well be worth it. My main suggestion. Don't go dressed as a penguin - ie use grey sports coat and pants, with white shirt, or use black coat and slacks with a coloured shirt... just make sure it is not fluro orange...
Interviews are largely psychological. Any boss worth his salt looks at everything. Are their shoes polished? Do they shine? What does their posture say? Did they bring a pen and pad with any of their questions? Do they write the answers down? Do they look me in the eye? Did they have a firm dry handshake? Do they ramble on needlessly, or do they know what they want to say, and say it? Do they take control of the room when they enter? Do they remain respectful? When asked to answer a question, do they hesitate?
There are millions of small things that your seasoned employer knows to look out for, if you face one of them, that little 'I am confident, I look professional' mask you are wearing for the interview will not fool them. If you are facing Mr Smith who is a librarian who also runs the local lyric theatre, you can get away with a clip on tie and a flanalette shirt.
Final piece of advice. Own the room.