This Seems like a cool plugin for PVP, it adds the unused potions into the game. You can craft them, but im not sure how. Link: http://forums.bukkit.org/threads/mech-fun-potionsplus-v1-0-unlock-unused-potion-and-potion-effects-1-2-5-r1-0.70053/
This would be cool, certainly, but people already complain about the use of potions in PvP (potion bombing). Allowing players to amplify and make them even stronger would receive lots of complaint from the PvP community.