I think the concept is great (events idea).
As you mentioned, there are many under Lvl-85-players. For the Horse-Race, I would recommend something not so far out that only high-level people can compete.
A thought: Race through Bree, literally through.
Last year, a couple Kinships got together with the idea of Angry Mob (sadly, I think it only happened once). Basically, as many players possible meet up at one spot, wearing farmer/commoner/serf couture, wielding knives/pitchforks/farm equipment, and promptly raid the countryside, cutting down everything in their path.
A couple of times, a few unscrupulous folk started summoning monsters in town. Although many were angered over this, I thought it was a blast (well, until the spawned them at player respawn points and inside the Auction House).
Just some ideas.
