The 2.0i engine is brand new this year and has been designed to give the base Impreza a huge jump in fuel economy, so it can match other cars in that class. The trade-off is a reduction in power from the 2011 base model 2.5i.
I have a 2012 Ford Focus with very similar power and fuel consumption numbers and I know it doesn't pack much punch, but it's pleasant to drive and very cheap to run.
The good news is that you bought a great car but, on the flip side, you did not buy a performance car.
I think it will be very difficult to get useful power gains from that engine. Realistically, SPT parts like their intake and exhaust don't really add much power even on the older engines, so my suggestion is to enjoy the car as it is