Yeah, I also think it is highly likely that the extra cost will outweigh the gas savings. It seems like Subaru is a little behind the curve in sveral respects. The stock engine on the Impreza is underpowered. They could have put the same engine that is in the BRZ. In fact, the Impreza should have the BRZ engine and the BRZ should have a turbo version of its engine. And due to the impending mileage regulations, everyone else seems to be ahead on engine development for high mileage. Nissan and Toyota have 2.5L V6s out now with 200ish HP for some of their mid-size cars and smaller SUVs. The 2013 Acura RDX will have a surprisingly efficient 3.5L V6 in it. The CVT transmission is a bonus but Subaru isn't alone there.
As an aside, I wasn't intending on buying this new. I am done wasting money on new cars. I think there is a sweet spot at 2 years old and about 30K miles. Most of the initially drop in value is done by then and you don't get a car with enough age or mileage where a bonehead who doesn't know how to maintain their car has done too much damage. I am looking 2 years out to when my son starts to drive and we get a third car. I am assuming we will be buying a 2012 in 2014. I could probably live with dog performance for the remainder of the warranty but would probably be looking to do something to improve performance and/or mileage at that point. Maybe an improved intake and/or exhaust plus a better tune would be enough.