Von, I thought we were talking about increasing your maximal strength and you won't do that at even 80%, you need to be up in the 90s or at your 1rm to do this. Getting your motor units all firing at once so that when you introduce the speed element you have a larger proportion of the muscle contracting.

Plyometrics are good but if you think your hitting a plateau then pushing your 1rm is one way you can go to improve. You need an experienced person helping you though.