Only just now listened to the ep where this was announced, so I'm late; also, I haven't yet read through the whole thread, so I'm probably repeating things people have said elsewhere. But I want to get my thoughts down before I lose them, so here you go. :-)
To me, a successful superhero story would find a balance somewhere between (say) the old Adam West Batman show and Heroes. Batman, of course, belonged to an older period of TV, where shows were usually purely episodic -- as my friends and I kept saying for Smallville, "what happens in the previous episode stays in the previous episode." These days you need growth and change and arc plot to keep people interested. BUT! Heroes, I think, shows how this can go wrong. Certain characters "grew" by getting more powerful, and the problem with that is, it can easily become silly; they start looking like Mary Sues/Gary Stus, and the scale of threat needed to cause trouble for them ends up being so over-the-top it's just not engaging anymore. Also, the show overlapped its various narrative threads so thoroughly that very few episodes felt like they provided any degree of closure; I enjoyed Heroes (for a while, anyway), but I don't think I could name off a single specific episode I'd go back and watch. Because none of them stand out from the rest.
The example I would pick, though it's from a totally different genre, is Supernatural. That show has its own problems -- missteps on the race and gender fronts, for example -- but the professional writer in me is deeply admiring of the way they balance Monster of the Week-ness against long-term growth. Most episodes are relatively self-contained narratives, but contain material that builds both character change and arc plot over the course of five seasons. And it does a nice job with the power curve, less for the protagonists (who mostly are just highly-trained humans) than for the threats they face, such that by S5 they've built to a pretty epic pitch without ever making a jump that seems unreasonable. They also manage, though not always quite successfully, to keep enough humour in to leaven the otherwise constantly-darkening narrative.
I've only heard about half of the Union Dues stories, so I don't have a particularly strong opinion on which specific characters should show up, etc, but I *can* say that character in general would be the thing that draws me in. An ensemble (a small one, not the giant and ever-growing herd of Heroes) with a strong dynamic, where the external threats they face both reflect and drive the characters' growth and change over time . . . I am THERE. I far prefer that to the solo-hero style of Batman or Superman. Heroes almost managed it, but never quite pulled together firmly enough for me to really get engaged.
