Unless the dealer wants to do a little trading, as in trade the newer impreza for a less desirable (from their perspective) previous generation impreza. Because if they have a car on their lot that is harder to sell, and can put a car on their lot that is easier to sell, they will probably cut a pretty good deal.
In NY (noobs on demands address) there are tax advantages to trading with a dealer vs selling privately -- as you don't pay sales tax except on the difference between the new car cost less the trade in amount.
As for the squeaks my car has a few, more in the winter (cold=everything expands and rubs a bit more).
Two are in the door speaker area, one is on the dash and pillar.
I have yet to address either because they don't bother me much, but all you need to do is pop the panel and put a little foam here or there to buffer the plastic, and for the pillar stuff a little foam between the dash and pillar -- the first requires only a little ability (but if you get in there, why not replace the speakers...) and the second is something a 5 year old could do.