What else could they really have done with Aang? Sure they could have him traveling around doing Avatar things like helping people, keeping the peace, and stopping baddies from doing bad stuff, but nothing would be able to be a bigger story then defeating the Fire Lord an stopping a 100 year long war.
Korra's story is going to be a very different story based the the first 2 episodes and the other little bits of info we have about it. In fact Aang are Korra are just about polar opposites. Where Aang never wanted to be the Avatar and was afraid that he would not be good enough to fill that role. He had to learn to be more confident in his abilities and become the hero the world needed to end the war. On the other hand Korra is too confident in her abilities and rushes headlong into any danger. I get the feeling the Korra will have to learn to be more humble and learn patience and that not all problems can be solved with brute force.
Heh, that kinda feels like a cheat. Like, "Hey you know those giant ten ton flying bison that no one has seen for 100 yeah? Well it turns out we found a whole heard of them!" Where the heck would even hide a bunch of them for 100 years anyways?