I didn't say you said decorative? Or did I? Well either way. I don't disagree with your answer, just adding some additional thoughts. =) Sorry, couldn't resist. It's LOTR.

The breaking of Saruman's staff serves to excommunicate him. It is a withdrawal of Saruman's divine authority, enacted by Gandalf, as the loyal earthly agent of the Valar.

Certainly a wizard doesn't need his staff to perform magic...but that doesn't mean the staff is symbolic. Anymore than the elven rings were symbolic. Clearly these staves are important to these wizards, and equally clearly, Gandalf is empowered to break Saruman's stuff in a way that Saruman was not so empowered. The wizard's staff is a vestment of authority, and the source of that authority comes from the Valar and ultimately, Illuvatar. and as Saruman was corrupt and fallen, authority was granted to Mithrandir. So I've always read between the lines, anyway.