I figured I'd throw this idea out to you: While 18's do look great, you don't necessarily need rims that big!
Here's what a member on my local forum did, see what you think:
The nice thing with keeping a 16" wheel size is your unsprung weight stays very low.
For example: an 02-04 WRX rim weighs 16.5lbs. A newer stock WRX rim weighs in the neighborhood of 20-22.
That pair of forged BBS wheels? 12.2 lbs. A set of 18's? 30 pounds, at least. Correct me if I'm wrong.
The other thing about running a 245 width tire (with a lowering kit) is that the wagons do not have the flared fenders that the sedans do. Too wide a tire, and the tire will rub against the suspension and fender, most often in the rear. Mess up a tire, and you got yourself a $120 toy for your kid to swing on.
Bottom line, the widest I'd go is 225.
My .02 cents