My wife and I married in December right in the middle of advent. The vestments were purple. there were not alot of decorations. The christmas tree is never put up until the feast of christmas, so that wasnt a problem. The music was appropriate. I dont really see a problem marrying in advent if its done with the season in mind. Our wedding mass was very spiritual and beautiful. Just as advent kinda reminds us of a new life and beginning, so does marriage. What better time is there to begin a new life at a time when the Church is celebrating a coming of a new spiritual life. We celebrate coming into each other lives completely at a time when the Church celebrates the coming of Christ into the world. I feel if you keep these ideas in mind, why not???Besides, like someone said, its not against canon law.