We have been considering and actually went to the Train Festival this past July in Owosso where the Pere Marquette is kept and operated. One thing I recently found out that has turned my mind a bit is that after you get to Saginaw, the Pere Marquette isn't the engine that brings you back, a regular diesel hauls the cars back. It has something to do with the ability to turn the engine around. That would be a big deal to my son, so it doesn't seem worth it. Another thing to consider if buying the tickets early: no refunds or exchanges no matter what the weather.
Honestly, I have heard that the "Santa Village" part of the trip isn't that great, it is all about the train ride (they put on a scene from the movie), with not much emphasis on Santa. Don't know if any of that helps. We have seriously considered it as my son is a HUGE Polar Express fan, but the uncertainty of the weather coupled with the cost and it is not so attractive.
mom to the amazing one 10/04 the wife 10/01