Thanks David, sounds like you are I have similar philosophies. Currently, i’m only doing about 30 min, 5 min warm up, 20 min run and 5 min cool down. I also do some slow biking (due to the more specific musculature most people recommend using a slightly lower heart rate when biking). For me, the goal is less about “fitness”, but more health focused. My personal workout goals are focused on kettlebells, but my high intesity workouts were draining me. My current understanding is that having a good aerobic base is the foundation of health and then you can add some intensity on top of that base.
Some of my inspiration has come from this old video of the Polish National Weightlifting team doing some aerobic work for what is arguably the least aerobic sport in the world. You only need to watch a few minutes. My favorite quote is “the exercise provides the oxygen needed for long hours in the weight room.” Clearly they do some varied, cross country runs mixed with calesthenics. (assuming this isn’t some propaganda tape.) http://youtu.be/SZgigENw8-g
One interesting point on improvements, i have read that you should test how far you can run at the same heart rate. As long as that is improving, stick with the aerobic work in the target heart range. Once you are not making improvements, start adding the faster, harder runs once a week while still doing aerobic work to maintain the aerobic base.