Interesting question, Mike. Unfortunately, it's most probable that the modern age crusade wouldn't work. First - the pope wouldn't call upon Christian soldiers, because the Church teaching is somewhat different than in the Middle Ages - there's much talk about ecumenism now, about shared values of monotheistic religions... and so on. If I remember correctly, Pope John Paul II officially appologised in 1990s for the Crusades, so I doubt if Benedict XVI would reverse words of his great predecessor and start calling for killing people in the name of God.
But... if it really happened, the effect would probably be pretty miserable. The pope is not an authority for Christians any more, he's just the head of the Catholic Church and his authority even in the Church is limited to matters of faith.
Having written all these boring and much-too-serious words, my answer to your question: "Do you think anyone would show up?" is "yes". I believe that there would always be a group of people (not necesarilly religious fanatics), ready to fight "for Christian values" using unchristian methods...
Bringing the