I think the amount of props does not really affect your mentalism, as long as what your audience sees is not your paraphernalia, but your MENTALISM.
If I was the spec, I wouldn't want to see you take out a notepad, treat it like something special, make me write on it, then wait while you read the impression I made on the notepad. What I want to see is you reading my mind, plain as that.
If your audience only sees props you want them to see, then that is the amount of props that you will want to use. If they see more than necessary, screw your props...or rethink the amount of stuff you bring to a show. As D ICE R said, he IS his favorite mentalism piece, because mentalists are Mentalists, not guys with props.