"Get a performance alignment. add some negative camber in back, futz around with the toe in (to the extent you are able; Subaru doesn't give you much to work with). My last Subaru was transformed by this, as it quickened turn in and made the car feel more "dialed in." This I will do very soon."
The rear camber is not adjustable, only the front, and if you want a "performance" alignment... you're gonna need some "toe out", not in.
"Springs- I am not convinced that the improvements just springs bring to the table are worth the hassle of installing them. Certainly not in my top 3 list in terms of importance."
IMO, second to tires, changing the springs can be the most effective way of improving the cars handleing. lowering the center of gravity and increasing spring rates would be the way to go. the FXT tends to "nose dive" excessively under heavy breaking and can be nearly uncontrolable on an uneven or bumpy surface. exiting corners can also be very tricky on the stock suspension considering the amount of front end lift resulting in nasty understeer.