Went for a 50 minute run last night. My heart rate didn't go over 150 over the entire 5.5 mile run, and there were a couple of times when I had to pick up the pace to keep my heart rate above 130. This is a considerable difference from even two weeks ago, so it appears my swimming workouts are having a big impact on my fitness level overall (I skipped one week of running to do just swimming).
That said, I think I know what I should be doing to change up my workout.
Plyometrics appears to be something that will help my comparatively slow muscles speed up. I got to watch a couple of veteran martial artists spar recently and even at ages older than 40 they are still very, very fast. While my lifting is going well, where my athleticism seems to be failing is in terms of pure speed, and thus plyometrics might do it. While I can (demonstrably) punch through wood planks (about 2" total thickness so far) all the power in the world won't help if I can't actually land a blow.
I'll start my search for plyometrics workouts this evening. It could be that my martial arts instructors have workouts just waiting for a student foolish enough to ask. We'll see. :)