Those Goodyear Duratracs are awesome in the snow, keep them on there.
Yup - when you can get $10-$12k off a new truck it's rarely worth it to buy used unless you go back 3-4 years.
I'd throw a set of Bilstein 5100's on all 4 corners, ASAP. With the maximum height set on the front for 2" of lift.