All of a sudden I have to buy lots of presents for other people, rather than myself and my bikes. So that's where my extra cash goes around Christmas.
I buy very little bike stuff for myself during the holidays, and stay away from Ebay. If my experience is common, then it would make sense that demand for vintage bike stuff goes down during the holidays, and prices would drop accordingly as there are fewer people bidding. Also, buying vintage bikes and bike parts is a very personal thing and hard to do for others - there are few of us out there who would have occasion to "gift" someone that Ebayed special vintage chainring, or NOS vintage hubs, for example. However, it would seem that those who remain bidding are those who have lots of disposable income and don't worry about cost (and are therefore able and willing to up and up the bids), so, I could be totally off base here.