If you want to go the WRX/STi route, then you have some options to consider:
How much money do you want to spend? Do you want to spend it all at once or would it be better to do it as-you-go?
Do you want to buy something more turn-key, or do you want to work on your car yourself?
Even if you buy a used WRX/STi, you still have to consider that you are unaware of what may be wrong with the car you buy, so you may have to fix a little or a lot of things.
If you get the WRX/STi, it will come with suspension changes not available on your current car, BUT you can modify your suspension with upgrades to be WRX/STi-like.
Get the idea?