Spreading contend out helps. Recently, in MoP for WoW, Blizzard spread vendors, raids, factions, daily quests, etc. Among every zone, instead of just the Level 90 zones keeps you moving in the world. I think it was pretty successful. For instance, a fairly difficult World Raid boss is wandering around a Level 87 zone, but can only be taken down by a large group of level 90 players. The boss thematically fits the zone (and doesn't hunt down players, thankfully), but still gives an incentive for players to get out and do stuff.