First you have to realize the 2013 is an older vehicle.
each year improvements are made, and the older ones for that
reason may not have the resale value. Most vehicles that are 4 to 5
years old are high milage and that also lowers the resale value. the
V-6 does have more HP but lower gas milage over the 4 cylinder
engine. I have a 2015 4 cylinder and get on trips over 30 MPG, In
town with short trips get anywhere between 20 to 24 MPG. The V-6
is between 17 to 23 MPG rated. That also may be a factor in the
lower resale value. I'm not sure, but the newer Terrains have a
different transmission, more speeds forward, which is better milage.
I still maintain, if GMC would drop a four cylinder turbo diesel or
even a 4 cylinder turbo gasoline engine to give more HP, it'd be a
win/win for the Terrain. A low milage, 2013 V-6 in great condition for
$12,000 is not a cheap price, Offer $8,000 and take it. The
difference in car payments will more that off shoot the cost of a
newer Terrain. Remember it is a used vehicle, but low milage so it
may not need much parts replacement. Maybe brakes and or
shocks, and a good tune-up. Enjoy it.