My aunt left a handwritten note saying that she wanted everything to go to me when she died but it is not signed or witnessed. Does it have any legal effect?

The Supreme Court now has power (since 1989) to give effect to any document that appears to have the intention to be a will. Evidence can be given of statements of the deceased about their intentions.
The case of the famous painter Brett Whiteley is an example of this where the Supreme Court accepted evidence by a witness to a handwritten will of its contents though it could not be found.