I was in the same boat as you too.
First thing is to ditch your 1.8L.
Most people buy the Impreza because of its AWD and handling. It's certainly not based all on looks. If you keep it a FWD, you will not be better than any other Civics IMO. But changing to AWD can be a PITA unless you have the tools/resources/time/knowledge to do so.
2315lbs.??? All the publications that I've seen on FWD base models are around 2400lbs.
It's true that AWD system will increase your weight a little and contribute to more driveline losses. Is it enough to noticably slow the car down? Don't know. Never raced side by side.
The older 2.2L engines don't produce much power at all.
Any of the newer 2.2L and 2.5L motors will require you to use the AWD tranny/system since it has a thicker shaft than the FWD trannys.
The best thing for a budget set-up would be to buy a whole wrecked Subaru Legacy Wagon from a Salvage yard. I've seen them generally go between $1k-$3k for the whole car.
You can use the 2.5L motor/tranny/AWD/larger brakes/rear disc brakes/struts/rear sway bar system/etc.
Go to my site for an intro: http://aspen.mwic.org/22lm