Creepers should have a bee-like social structure. Standard creepers and maybe lil' creepers are the drones, maybe big, soldier creepers that guard the nest and the big matriarch Momma Creeper, who's too fat to move quickly but spawns lil' creepers to guard her. They could have explosion-proof nests to generate every so often.
Of course, if this happened, other mobs would need attention too, like maybe slimes that spawn normally again or spider lairs with spiderlings or evil obsidian Skeleton Towers with a king skeleton, garbed in gold armor.