Sport specific training for martial arts ( plyometics/power)?

It sounds like you already know quite a bit about plyometrics. Leapfrogs and running stairs definitely helped increase the speed and power of my kicks. One exercise that also helped me was weighted knee lifts. Put 10-15 pounds of ankle weights on one leg, then while standing raise your knee as fast as you can (as if you were doing a knee strike). Do sets of 10. This will speed up the chambering phase of your kicks. You can also strap 5 pound ankle weights on your wrists and shadowbox - that will speed up your punches.