Some zones are less populated than others. This can make playing in that zone considerably less fun, especially in the high-level areas.
How about instead of having tons of “new content” every month, simply change the rewards in those zones occasionally (and temporarily). Similar to GW1’s having the Traveler wanting certain items only available from that zone (or, a couple of them at a time).
I’m not talking about game-unbalancing stuff, though (which GW1’s Traveler gifts did alter somewhat). More like one week you have an incentive to find 5 items that just happen to only drop in certain areas of the map. A scavenger hunt.