A 1998 model is just about 8 model years old. At 25K per year, a 98 might have 175-200K at this point in it's life. I disagree that 173K is high.
However, that Caravan is another problem looking to happen. They also suffer terrible tranny problems and AC systems are also prone to breaking.
The ONLY reliable mini-van that can be had at a "bargain" price is the 2000-ish Mazda MPV. For some reason, they depreciate LOTS. You'll pay top dollar for the Honda or Toyota, and it's because they're the cream of the crop. The Mazda is the only non-Honda/Toyota worth investigaing in the segment. And yes, I thought of the Quest in that statement. It has a poor rep, too.