Emerald tipped arrows would give more damage and shoot farther. If a sword can be upgraded to diamond why can't the bow? I know you can enchant it but so can a sword. This would improve dispenser shots and archer’s strength.
You're on the right track, because ranged combat in minecraft needs more variety. But to be honest it doesn't feel right. Emeralds are quite hard to get/keep depending on your style of minecraft play. I don't think anyone would want to spend them on arrow crafting
http://www.minecraftforum.net/topic/1401777-earn-a-good-or-evil-reputation-with-the-villagers/
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