This is a nifty little plugin made by a developer of a server I used to play on, it automatically enchants an item based on usage (you can define levels in the config file for different items).
It’s getting on in age now, and I’m not even sure if it still works. I also don’t know if you can even accomplish this with Sponge yet… Nevertheless, I thought I’d ask, it might interest some people.
Github: https://github.com/PrecipiceGames/AutoEnchanter
Bukkit: http://dev.bukkit.org/bukkit-plugins/autoenchanter/