A fork in the road
I plan to run a "good" volume of mileage at an intensity which is at or below the 'Maximum Aerobic Heart Rate' as described by Phil Maffetone in this article. For me, this is running at a heart-rate of 130 (or lower) — around 78% of my maximum heart-rate. Over time (hopefully) I'll see an improvement in aerobic condition. My running speed at that heart-rate (and higher heart-rates) will become faster.
At the same time (if it's not too stressful), I'll do a small amount of training to work on my glaring "top-end" speed problem. Things like short/steep hill repeats, 100 metre fast strides, and running drills. I'll also run a few of the ACT Vets' Thursday evening track races — most likely some 3000s and 1500s.