What is the significance of seeing it again? Although it is interesting as a matter of historical curiosity, the real significance is as a visible sign with continuity with the past. It is especially fitting in this "Year of Faith" and 50th anniversary of the opening of the Second Vatican Council as it highlights Pope Benedict XVI's emphasis on a "hermeneutic of continuity" in interpreting the council as a continuity of tradition rather than a break with tradition.
On a personal level, there is also a tender feeling in pulling out an old garment with its own history and wearing it during divine service. There is something comforting in knowing that "Father so-and-so wore this back in the day." It gives you a feeling of connection with the faithful who have gone before and with that faith they believed, taught, and defended.
The fanon worn by the pope on Sunday was probably new since popes are buried in the garment (though I don't think John Paul II was). But the feeling is the same--joining with those who have gone before us in a shared life of faith.