The reason why we keep getting movie "reboots", "re-imaginings", or the like, is simple: origin stories are both predictable and comforting.
In an origin story, nine times out of ten we know -- or at least have a good idea -- what the end of the movie is going to look like. Tony Stark will be Iron Man. Mad Max will sail off into the sun set. Peter Parker will be Spider Man.
And it is this predictability that we find comforting. We enjoy the details of the road to our ending, and the twists provided in those details are not seriously damaging to the potential of the expected end result.
This even extends to virgin franchises, to movies set in universes we know nothing about. The origin story is about the protagonist discovering himself and his place in that universe, and we go along with that discovery. The discovery is itself an integral part of the story, and of the experience of enjoying that story.
The problem with a sequel is that for the most part the discovery is over. Tony Stark is Iron Man. There isn't really anything new to learn about him. The fact that we know this hero and this universe is itself a trap, because having discovered the universe, we run the risk of not discovering anything worth the time during this second trip through it.
The result of this is one of two things. Firstly, the custodians of the franchise do provide something new for the audience to discover. Stark's poor (and poorly understood) relationship with his father. His father's relationship with the co-inventor of the arc reactor. I'm not saying that these things are themselves worthy items*, but that's what is presented.
The other, far more common result is that the custodians indulge in what I describe as "kicking their characters". They try to crank up the danger that the characters are in, they subject them to harsher trials, all in an attempt to keep the audience engaged. Think Spider-Man 3 with two or three enemy characters. There was so little actual content in the movie, the producers had to fill it with a second bad guy. The problem here is that this is not the trip that the audience signed up for. They wanted another comforting trip through a world of discovery, and constant, amplified peril is something completely different.
(This is also why many TV series "get bad" as they get older; once the majority of the discovery of the characters and universe is complete, cranking up the crisis level is left as a poor substitute.)
So. Based on this, I don't think we're going to see a drop off in the number of series reboots. The movie going public wants something predictable and comforting, and that's what Hollywood is going to give them.
* even though I personally think Iron Man 2 is one of the better movies in the Marvel pantheon.
