Should I lower my Impreza/WRX?
That's up to you. There are a lot of rumors about how you "shouldn't" lower an Impreza because the factory has some magic perfect suspension settings and you'll just make it handle worse. This is not true. Lowering an Impreza has the same benefits as lowering any other car. Lower center of gravity and less body roll, which means better handling. Plus, it just looks cool
The thing you need to remember when lowering an Impreza or ANY car, is don't go TOO low and don't go TOO stiff. Any suspension requires a certain amount of suspension travel to work right, and if it's too stiff it will bounce around too much to handle well. Your best bet is to go with a coilover spring and strut combination, Tein makes kits for the Impreza at reasonable prices. If you can't afford a full coilover setup, springs alone can offer some benefit, as long as they're designed right. The best way to make sure of that is to simply buy from a reputable manufacturer that know's what they're doing, like Tein or Whiteline for example. Stay away from the cheap "coilover conversion kits" that are just a sleeve that drops over the stock strut.