"Do you think I should be leary of buying a focus wagon with 170K on the clock?"
Yes. Very leary. No, strike that. You should be very, very, very leary.
The Focus engine works rather hard and I would be Extremely reluctant to buy a Focus with that many miles. In fact, the only way I would buy one with that many miles is if (a) I couldn't come up with the money for anything lower mileage and need transportation, or (b) it was dirt cheap, I was only going to use it for short trips as a secondary car, and planned to fix thngs myself when they broke.