New Goals for the time-efficient lazy person

My running of late can be summarised by one of the two descriptions below:

a) one mile warmup, two to four sets of 400s, one mile cool down
b) 20-30 minutes jog

I will be focussing more on speed at the shorter distances for many reasons. One is because this year I expect to do a bit more commuting to and from work and time will be a premium. Another reason for this is that I feel if I wish to run faster for longer distances (who doesn't?), then I should work on speed for, say 400m, then work at maintaining that speed for 800, then a mile, then 5K etc. No brainer, right? A third reason is that I'm simply lazy and don't like to run for too long. Running is one of the things I do outside of work, but not "The Thing". I'd like to keep it that way. Fourthly, I'm more proud about running a 70-second 400m and a 2:45 800 than a 36-minute 5-miler.

In the past two years I have set myself the lazy person's goal of achieving 50 runs between September and Christmas, but this year I will not be doing that. While it's been good to have this 50-run goal, I feel at times I've done running more for the sake of ticking off the runs on the 50-to-do list, then actually making sure that they contribute towards something helpful in the long-term. These next three months I'm going to focus more on weights, stretching, and working up to maybe 8 sets of 400s in 80 seconds.

How does walking affect cardiovascular health? I wonder if there have been any studies about the effect of regular walking (not brisk walking) on one's running ability. Many years ago I walked daily to college, forty-minutes each way, 5 days a week for about six months. The first time I decided to run after that, I ran a half-marathon in 2:35. I now walk about 2.5 miles six times a week and wonder if I can use that in some way - maybe it compensates for one less session of running? Hmm.