There is new study out that challenges some older beliefs about weight training and strength. I will try to find the study and post a link to it.
My summary: A group of ninety young men of about equal fitness was divided into three groups. The the fist group worked out using a regime of one set of 5-12 repetitions using enough weight to achieve total muscle fatigue. The second group did 3 sets using enough weight to achieve total muscle fatigue. The third group did five sets using the same criteria: enough weight to reach total muscle fatigue. The researchers found the five-set group had the largest muscle mass gain while, the single-set group had the least amount of gain. The three-set group's muscle mass gain was in between the other groups. The strength gain differences between of the 3 groups is what surprised the researchers; there was no significant difference.
I disagree about upper body strength not being significant in endurance sports. The first thing my daughter's track coach did when she entered college was to put her on a weight training program - she was (still is) a distance runner. Core strength is important in any sport.
I have used weight training since high school, and still hit the weights 5 days a week at 75 years old. I was an endurance athlete into my mid forties. My best events were the 50 k and marathon. I did run one 50 mile race to qualify for the Western States 100, but did not compete in that event. I could bench press 185 lbs, and the weights used in the other exercises were proportionate. I could never build any muscle mass that amounted to anything, but I thought I was pretty strong for my weight. I use a regime that has been modified over the years, but it is essentially a cross between the between the first and second groups' regimes discussed above. I also cycle or spin daily, and ride about 4,000 miles a year. My wife and I have toured over 20,000 miles, totaling 20 months, through 11 countries since 2007. I do agree that going to the gym may not always be beneficial. On the way to the gym last Monday morning, I dumped my bike on the ice and have a sore shoulder, forearm, hip and knee to show for it. Going skiing yesterday didn't help either
At 6' I weighed between 150 lbs. and 160 lbs. most of life, but have dipped to 145 lbs when training hard (running 60-70 miles/week+ weights 3 days/week), or riding multi-month bike tours. I have always felt that my height /weight ratio was an advantage not a handicap. I've also participated in other sports including : judo, bike racing (mediocre), rock climbing, mountaineering, and telemark and xc skiing where being tall and skinny didn't seem to matter.