We are most definitely looking into making major overhaul changes to the AMV contest for 2012. However having different skill levels is not likely going to be one of the changes we make. Mainly it boils down to what different ability levels would achieve and where and when we would place them. The main AMV contest over the years has developed into one of if not "the" most competitive and respectable contests in the world to be accepted into. This past year we had 18 countries represented and we look to add onto this in following years. When videos are placed into the contest, they are put there because the judges feel they either have exceptional quality or creativity merit, or have exceptional audience entertainment potential.
We have also seen that simply due to an editors beginner or advanced ability has no bearing on their ability to make a video worth being in the contest.
For reference, several years ago the video "As thin as paper" was made by a local editor and it was his first video and not only made it into the contest, but won the asuka for Judges choice.
http://www.animemusicvideos.org/members/members_videoinfo.php?v=128710Then of course is where we put it, as has been pointed out, we do have the AMV Overload event to showcase as many videos as we can that are submitted. Back in the days when I ran the Fanime Con AMV contest, I was given a large room for two entire days to show videos, by having access to this we were able to show all the videos sent into us. However my belief is such that there are conventions that have dedicated AMV 24 hour rooms, and this is just too much to be showing at one event and everything becomes a blur and nothing is special. ( Hey maybe that's why I named it AMV Overload )

NDK tries its best to put as much variety of content as it possibly can for the sake of its attendees, making one event or another have too much content could overshadow or push out other events and I'd rather not go down that path.
Of course the hidden reason is also one that Pwolf pointed out, we want editors to strive to make something better each year. Making the contest less difficult and challenging to be apart of would be counterproductive to our ongoing goal of hosting the best AMV contest in the world for our attendees to enjoy. There are dozens of world class editors that watch this forum board that are desperately trying to give as much advise as they can to help editors improve to make the contest even better.
However I will say that nothing is written in stone and I always want as much feedback and ideas on how the AMV programming at NDK can improve.