I
do pay attention to mileage, as it's my DD. I don't know why the ratings are so low, but I typically drive I'd say 60% back roads and 40% highway and am getting around 23.5 for the most part. Like said, on road trips (all highway) I can get 26+ depending on the terrain, traffic, stops, etc. etc. It should be noted that I'm getting this mileage by driving conservatively, staying out of boost for the most part and not putting the hammer down. The few mods I've done haven't seemed to affect the mileage, really. Some people claim they've gained mpg's after doing similar mods, but I haven't seen it.
Hope this helps

. Like said, I love the car and plan on keeping it for quite awhile
EDIT: Should also note, I don't know your age, but insurance on it is very reasonable (In my case at least). I was looking at WRX's as well and the insurance rates were
much higher on them, I suppose for obvious reasons.