I have a 2010 Forester. Its starting to get a saggy butt. Id like to be able to put more stuff in it for longer trips. Also want to put a tow hitch on it and mount the spare back there. So, can I just upgrade the rear springs and be fine? Or should I do the whole suspension kit? Ive already got 10.5″ of ground clearance, so I dont really need a lift.