Fisky, I agree with you. I don't think I do enough shorter, faster stuff, but whenever I add 6-8 x 30 seconds hard, my stride feels better the next day.
I, too, was forced to take a year off from running, and when my back relented, I returned about a year ago. What I remember is that it was hard--weirdly, surprisingly hard--to get much below 9:00 pace, even when warmed up. But slowly, over the weeks and months, that speed came back. My midweek runs often took the form of progression runs with a fast, or faster, last mile or two. And bit by bit, those high-end miles speeded up. 8:45, 8:35. I run a hilly 8-mile loop sometimes, with the hills in the middle and the last two miles rolling gently but consistently downhill. I used those downhill sections to recoup my stride length and form.
Last spring I ran a series of 5Ks, with 7:47 pace as the best average. Still, when I'd do 6-8 x 30 secs, it was hard to get to 7:30 pace. Last Wednesday, though, I had a sort of breakthrough and average 7:08 pace for 6 x 30. That's basically my current one-mile pace. It feels impossible to go much faster than that right now.
BUT: two days ago I ran a 5K and all the pieces came together. I ran 7:52, 7:56--that middle mile was up and down a couple of low hills--and then threw down a 7:34 on the final mile, with zero form issues, feeling smooth, averaging almost 97% of max HR for that mile, and ran (my Garmin tells me) 6:33 pace for the last 40 seconds, hitting max HR of 185 as I crossed the line.
7:44 pace average. Average HR of 175, which is 95% of max--and a notch or two above the average HR of every race of this past year. Mission accomplished.
Part of the mix that enabled this flat-out performance was clearly those faster strides. They smoothed out my high-end stride, so that, rather than pushing the limits of my form in that final mile, I could focus exclusively on pushing to the limits of my heart's ability. I know I did this because I felt nauseous for a few second right after crossing the line--something that almost never happens, and something that indicates a truly flat-out finish.
So yes, you're onto something. I would urge older runners to give the speed-recuperation process the time it requires. Keep pushing at that edge, striving to roll it back bit by bit, but don't hurry it.