What are best workouts to improve your 200- and 400- meter speed?

After the hill workouts (not sure exactly what type of hill workout you are doing), do 3-4 10 second sprints up the hill, and over time build up to 8-10 of them. These will build speed with less chance of injury.

Also add in strides after easy runs on the track. Drills can help too, as can doing some lifting for the quads/glutes/hamstrings in the gym. Careful of the injury bug and take an easy day after a new stress. You may be sore after some of these things, just wait it out and you should adapt quickly.

appreciate input...the hills are up college stadium ramp - very steep and about 100 meters...I run them pretty hard and up to about 20 now - eventually would like to do about 40

Personally, I would keep them at 20 and increase the intensity gradually rather them the volume. 20X100m is plenty and the main purpose of the hills is to build speed rather the endurance, so keep the volume down and keep them at maximum effort.

weights

core work

weights and core? - I do tons of ab work - but weights? I do lots of lunges with 50 pounds and squats - what else?

5-6 x 40m all-out w/ 3 minutes slow jogging recovery once or twice a week is a good way to improve real top-end speed (which will help to improve your 200- and 400-meter speed, as well as all distances on up the ladder).

Do things like 12 x 60m @ 400m pace. You really want to ease into this type of stuff.

Increasing max strength will help as well.

Keep up the hill work.

plyometrics for geriatrics