Of course people should build up their strength and ability slowly and steadily, in weight-training as in running. But when you have developed a base level of muscle tone and know how to perform the exercises correctly without "cheating" and doing full range movement,it should be no problem to plan to develop your strength and endurance to the level you want. A pound of of extra muscle will store more glycogen than a pound of fat Also when the body uses up its glycogen store, it starts to convert protein [muscle] into energy before its fat store. Thus lowering the base metabolic rate. That is why it is important to build and develope muscle tone.
I agree with the writer, especially about good muscle tone burns caloriies even while resting. But when working out in the gym, it seems to me that many people lift so light a weight as to make no difference. I was taught that on a leg press machine, where you body weight is supported, you should be able to do 3 x 10reps of twice your own bodyweight. Why? Because when you climb the stairs, you are lifting your whole bodyweight on one leg. If you build up your leg strength to do 15% more weight, you wont slow down on the hills.
I've never done the Torbay half. I did the Bideford Half this month. But good for you sfg. I started running 6 years ago to get fit. My saying is "you can't stop getting old but you can stop being doddery!". I am 63 now. My running has slipped a bit the last couple of years but I am just getting back into it.