I have found on my wagon that adding a rear sway bar, or going larger in the rear, is a much better way to improve handling. Increasing the front bar will increase understeer and the wagons already have way too much understeer. Increasing rear bar size will decrease understeer.
I currently have the matched front and rear Hotckkiss bars on my wagon and have to say they are excellent for handling. I haven't taken the car to the limits, but it feels almost at neutral but a bit to the understeer (safer) side. They are huge at 1 7/16 front and 1 3/8 rear, but they are hollow. Hotckkiss claims they are the same rate as the old solid bars which were smaller, but heavier.
They aren't cheap, but I would buy them again in a heartbeat as they are very good at what they do.