If you can wait until late January / February, it is probably worth your while. I noticed a fall-off in resale value on my own car (based on ads that I saw in the paper) of just over 1000 euro. I would expect the car to lose value of about 2000 to 2500 over a full year.
Its also worth bearing in mind that the ads may not reflect the final sale price of a car. I wouldn't be afraid of ringing a vendor and offering them less than advertised because the car will be a year older in Jan. If its a garage, they could be keen to get the car off their books before year end.