I think this may be linked to a related problem I'm having with a specific World Encounter: the Revelers. I've run across the three Revelers randomly in my travels a few times, but I never completed their mini-quest because I never had the required item on me. I wasn't even aware of the quest involving a specific brand of mead (and the useful reward they give the player in exchange) until a friend brought it to my attention.
Normally this wouldn't be a problem, as I usually run into the Revelers partying at random locations to the side of the road as I travel across Skyrim. Unfortunately, for the past real-life two weeks the three Revelers have been standing around on the property of Pelgaia Farm across the road from Whiterun. They stand there day and night just idling, not displaying their party animations, and not responding with anything more than a generic greeting when approached. And since then I have never encountered them randomly on the road anywhere else anymore. It has been over two weeks of real time now and they're still just there after 100+ hours of play. And because of this I can't do their little mead-exchange quest.
Now, I think this is related to the problem with World Encounter points drying up because the last time I ran into these Revelers they were at the World Encounter spawn point near the road just east of Redoran's Retreat. That's just down the road from Pelgaia Farm, which is where they apparently ended up after packing up their party (once they give the player a drink they stop their party and start journeying down the nearest road). This specific World Encounter spawn point stopped producing random events from that point forward. I suspect it's because the three Revelers are still "active" and currently linked to that spawn point, preventing it from spawning anything else.
Here is a link of a screenshot I took today of the Reveler's, where they have been standing around Pelgaia Farm for two real-world weeks (and 100+ hours of game time) now. As an amusing side-bug, when I went to take this picture a dragon spawned near Whiterun and is just circling over my position (that's what all the Revelers are staring off at in the picture). The dragon refused to land or attack anyone, despite having plenty of targets. This not-so-rare bug was supposedly fixed in the recent patch, but obviously isn't.
Image: http://farm8.staticflickr.com/7171/6439263611_6a841d9c21_b.jpg
Please fix this problem. I'm slowly running out of working World Encounter spawn points.