You will do better if you sell your old machine privately since when the dealer sells it he has to add in a profit over what he gave you for it. Usually, you will have no problem finding a buyer for the machine, and you will get more for it in a private sale than you will in a trade.
When it comes to buying new, shop around to find the best deal. Keep in mind that spring isn't that far away, and right now the dealers are willing to make better deals on spring equipment while there is snow on the ground than when the grass is turning green. Also, at the first of the year, the prices are going up again. Rumor is 6-8% so inventory in stock now will sell out quickly. Once the new prices go into effect any inventory remaining in stock will go up in price as if it had come in after the price increase. In 8 more days, the days will start to get longer, so spring is only about 97 days away. You snooze you lose.