You could probably learn J2ME faster, but in terms of career there isn't much growth. you know one technology and aren't able to get any other type jobs.
With J2EE, there are Web, Business Services, and learn more architect type work as you go along. I think it also allows you to use J2ME in part of the architecture without being pigeon-holed as a J2ME only person.
J2ME is only slowly starting to pick up a little in the job market. But there are still few jobs out there. About a year ago, I would say you couldn't find any. Now there are about 3 to 4 positions in an area.