it really depends what you are looking for. first off, a stiffer car is a less forgiving car. so any time you stiffen the car you make it easier to spin out and lose control. chances are you cant drive the stock suspension to its limit and thus you are the limiting factor in your cars cornering ability, im not making a personal attack here im just playing the numbers.
that being said, the greatest benefits the average driver will obtain from suspension upgrades is an altered driving experience. The wrx has gobs and gobs of understeer stock, its like that because understeer is far safer then oversteer.
if you ultimate goal is to be able to take turns faster, go take a driving school. when your skandi flicking your stock sube around town come back and we can dissect the living shit out of some suspension upgrades.
if your ultimate goal is to have the most comfortable driving experience. change nothing, and go take a driving school.
if your ultimate goal is to have a little more fun while driving in a spirited fashion, e.g. sliding the car around and/or not being hampered by easily induced understeer, get the rear sway and endlinks and go take a driving school.