Two things. Starting with your last point, once they get together there is plenty to do like saving the cheerleader and saving the world. I personally don't see the purpose of this show being a bunch of supers wandering around aimlessly with the big payoff at the end of the season/series being them getting together at the same time and knowing each other. If that is all there is it lacks the something special to make me care. As for your first point, The shows you mentioned all had great season long/series long arcs. They also had episodes that stood alone and had purpose individually. I would be much happier if some of them got together and started doing thing together that lasted just an episode or two with a real payoff, but like DS9, or Farscape, or B5 meta plots elements would still be introduced.