I think the biggest asset of the Focus wagon is its size. Bicycles, skis, etc. fit very easily inside and with the split seat, there is still room for passengers in the back. I've never needed the roof rack (except for small boats). Keeping stuff inside reduces both vehicle drag and likelihood of having your gear ripped off. I have transported several 4x8 sheets of plywood in my Focus (they go in diagonally). You can't do that in a Vibe/Matrix, Golf, Saturn, or Mazda 3. Honda and Nissan don't offer anything in a small wagon. Some of the Korean cars might be cheap and roomy but they don't appeal to me.
You could get the same cargo room from a bigger, more expensive car (like a Subaru, Volvo, Audi, etc.) but you wouldn't get the same fuel economy. On long trips, I get around 6.8 L/100km (34.5 miles per US gallon). In spite of what some people say on this discussion group, I have found my car to be relatively trouble free and very cheap to operate. It has seen five Canadian winters with salty roads and -30=B0C starts. It still looks good and has not let me down yet. The 2.0L Zetec on the 2001 Focus is totally adequate power-wise for me. Note: my previous vehicle was a VW Westfalia so I'm clearly no horsepower junkie.
I would buy another Focus, although I probably won't because by the time I need another car, I expect there will be something more up-to-date. I just hope it can carry the same amount of stuff.
Steve