Fin Fang Foom wrote:
I wonder if a key part of this problem isn't that, for the most part, the only people left who have an interest these characters to begin with are the same people who had an interest in one of the previous incarnations.

It often seems like the biggest selling point in this sort of situation is, inevitably, that it's the relaunch of a licensed property -- and sure, I understand, that's an attempt to build on whatever equity there might be. But the problem is, by this point, that might not be much. 
That's why I think it's odd to see so many licensed comics again:  Green Hornet, John Carter, Six Million Dollar Man, THUNDER Agents, etc.  Nostalgia works for movies and TV because the audience is that much larger, both in terms in of lapsed fans and potential audience because of the widespread availability of format.  New comics based on old licenses already have to deal with a shrinking comic audience.  Many former fans have left the hobby.  Comics are already limited by their distribution to the Direct Market.  Add to this the fact that most publishers throw these comics out with little outside advertising/promotion means that most of these licenses won't last long. 

What would be considered the most successful and enduring comic license?  My guess would be Star Wars (especially under Dark Horse).