There is already several public areas in spawn that allow players to obtain mob drops.
(Xp, bones, rotten flesh, arrows, food, leather, feathers... are obtainable through /warp xp or /warp food)
However, one of the most useful mob drops was left of this list, Gunpowder.
Gunpowder has several unique uses in this game.
TNT, firework rockets, firework stars, splash potions, and fire charges.
So as you could suppose i am supporting the idea for a public creeper farm.
Please consider this idea as I'm sure lots of players would appreciate the idea of a public source of gunpowder.
Just like warp Xp but unique to creepers for the collection of gunpowder.