I see lots of posts about rear sway bars, shocks, springs etc but I just wanted to say that I think the first thing that any spirited Subaru awd driver should do is increase front negative camber. The front already has bolts that are adjustable, so it only costs the price of a wheel alignment. Or wait until the next time you need tyres and its free!

OEM bolts can get you between -1.2 to -1.5 degrees of camber. This is enough for most street cars and you will not see much increase in tyre wear or anything at all. Above this amount of camber you will need to get whiteline camber bolts but this is mostly for the track and you can start to see uneven tyre wear on the street.

As we all know Subaru's from the factory tend to understeer, increasing negative camber helps the front turn in and reduce understeer. It is much better to get the front turning in than trying to push the rear out around it. The first modification seems to be a bigger rear sway bar, while this 'can' still be a great mod, I would suggest increasing the front negative camber is more important and should be done before the rear sway bar. Bang for buck it doesnt get much better. Big rear sway bars can have issues with lift off oversteer, mainly in the wet.

This is not saying other suspension mods wont help as well, but I think this should be number 1 priority, then decide what to do next.