I've run a bunch of marathons, though I have limited experience in long distance hiking thus far. Beyond being fit weight and cardio-wise, I agree with 10-K that knowing your body and what it is and isn't capable of is an advantage. I agree with the school of thought that once you get to a certain level of fitness, the mental aspect of any long distance or endurance endeavor is critical to not only performance but enjoyment. I expect having multiple experiences of having pushed my body and mind for a long time after fatigue sets in would be a big advantage in a long distance hike - especially as compared to someone who had never before been to that point physically or mentally.