I found this neat study(pdf) that compared low and high-intensity strength training in older men. The low intensity group used repetitions of 14 to 16, while the high-intensity group used repetitions of 6 to 8. A 24 week training program was followed by a year of detraining.
Amazingly, after a year of detraining, the high-intensity group still maintained some benefits of the strength training. For example, their performance on the leg press and chest press was still above baseline measures. In the low-intensity group, most values returned to the baseline measures.
To me, this shows that high-intensity strength training is powerful medicine. It also shows that it may not have to be performed as often as some people think. High-intensity training leads to structural remodeling in the body, and these changes won't fade in a week or two.