Hey Skedaddle, my lower leg would get very tight and I never did much about it until I got really bad top-of-the-foot-pain. Now I religiously massage the lower leg, front and back, with a marathon stick and a spiky stick, and stretch out my feet and my legs, and this dual approach has helped a lot. I'm about to incorporate some foam roller stuff into my routine too (you can get a 12" one for $10 with Amazon Prime, or a 36" one for $23--so it's not really worth going the hardware store route unless you think a harder pipe is more effective [I made a nice t-bar for kettlebell swings out of pipe for $10, so I like the low-tech approach when it's equal or better to purpose-built gym equipment(see Kemme Fitness for more ideas)]).
I also think speedwork might speed up the process of speeding up, but I think no matter what you do you will keep improving. An 8mm pace is quite a reasonable expectation for someone in their 50s. That's my impression anyway; lots of older folks do 3:30 marathons, right? Right now an 8mm pace over an hour's time (about 7.5 miles) is my immediate goal. I'm attacking it by running over an hour at 9-10 mm pace, and then doing fartlek runs (with walking breaks) at faster paces, as well as hills once in while, both for an hour or less. I think I'm making progress.
I also think speedwork might speed up the process of speeding up, but I think no matter what you do you will keep improving. An 8mm pace is quite a reasonable expectation for someone in their 50s. That's my impression anyway; lots of older folks do 3:30 marathons, right? Right now an 8mm pace over an hour's time (about 7.5 miles) is my immediate goal. I'm attacking it by running over an hour at 9-10 mm pace, and then doing fartlek runs (with walking breaks) at faster paces, as well as hills once in while, both for an hour or less. I think I'm making progress.