I'm torn with this. Because as you said, continuity serves for character development, but I really really REALLY want self contained franchises, developed just like TDKT. Right now, I don't really care for a Justice League film, I just want epic stories with the most important characters of DC. We had that with Batman, I just hope that Man of Steel will be good and do well at the box office so we can have some well done Wonder Woman, Flash, Green Lantern, films. I believe even Aquaman can sustain his own film.
But Justice League seems inevitable, so if you they are going to make it, just make it good. I do believe that it loses something by not having established characters first. But it can work. I mean the Justice League animated series had only established firmly Superman and Batman, (with guest appearances from Flash, GL, and Aquaman). And it turned out great. I'll keep saying it, having the animated series as template is a step in a good direction.