I made a post last month talking about how the reason the star system has declined ("Star system" is a way of saying, the ability for an actor to single handidly guarantee an opening gross based on his name power) was that the actors used to be the brand, and now the brand is the franchise film. The importance of the brand hasn't declined, it's just what audiences associate a brand with most powerfully has.
I was watching an ad for Snow White and the Huntsman yesterday and it dawned on me "What was preventing them from just casting Robert Pattison in this movie", thus with Kirsten Stewart, reuniting both Twilight leads. As far as I can tell the move would've been all upside. Best case scenario is the Twilight fanbase all sees it, the media makes the film a much bigger deal, and it opens to a franchise creating 100 million. Worst case scenario is not that Pattison hurts the gross, only that he doesn't help it - In other words, it likely would've struggled anyways. I don't see any justification that casting Pattinson would've actually put anything at risk in terms of its opening. It likely makes more, the question is how much more.
However what this tangent led me to thinking is how bizarre it is that Hollywood never reunites pairs from star movies with the direct attention of grabbing the fans of the first. To me this would be a solid move, because the pair's chemistry in the first created a brand of sort, which pulls in the viewers to the second film. In my lifetime two examples of huge hits based on this premise is You've Got Mail reuniting Tom Hanks and Meg Ryan after Sleepless in Seattle's breakout, and Runaway Bride doing the same for the Pretty Woman pair Richard Gere and Julia Roberts. And both of those were massive hits. Also they seemed to understand this deep into film's past. Fred Astaire and Ginger Rogers kept acting in movies together because that's what sold. Furthermore, as far as I can tell repeating star pairs is a habit Bollywood uses to maximum effectiveness.
For example, in 2009 the Proposal with Sandra Bullock and Ryan Reynolds was a huge hit. Would it have not been a sound decision to cast them both in a follow up romantic comedy in 2010 to 2012. It would not have been without risk if the concept and ads weren't up to speed, but no film is without risk. As far as I'm concerned though, putting together that pair would've given it a leg up on any romantic comedy released in the following years, and would've given it the brand power to anchor a 30-40 million opening weekend in a summer. Other possible pairings off the top of my head include reuniting Ryan Gosling and Rachel McAdams to capitalize on the Notebook's success or Robert Downey, Jr. and Gwenyth Paltrow's chemistry in Iron Man 1 and 2. And why hasn't anyone put Brad Pitt and Angelina Jolie back on screen together with their noteriety and after Mr. and Mrs. Smith's success based off of it? You can even extend attempts like hiring Tobey McGuire and Kirsten Dunst in a romantic comedy, getting Daniel Radcliffe and Emma Watson together (to satisfy the "Harmoine"s), or plenty of other creative ideas. Going for same sex pairs, maybe Tom Hanks and Leonardo Dicaprio make another movie after Catch Me if You Can was so great. Worst case scenario for these films is no worse than pairing random combinations of stars that haven't proven their chemistry to the audience. If it dies, it dies. But as far as I can tell reuniting a star pair is an almost all upside maneuvre and could single handidly give a reason for these products to get talked about and launched.
Perhaps this is the next step and evolution for the star system. One star doesn't cut it anymore unless his name is Will Smith, Adam Sandler, or Denzel Washington. People don't care about the actor individually as much as they used to, so it's not enough. But maybe if they start making brands out pairs of actors, if the brand extends to their interactoin and chemistry, it can come back. The Avengers in a way may even be a comparison showing this. The reason the Avengers was so great a hit is that Iron Man, Thor, Captain America and Hulk were established brands and characters, thus the idea for people of coming to see them again, let alone together, was freaking awesome. No, not every company can pull an Iron Man and Thor out of their hat, but perhaps reuniting a Ryan Reynolds and Sandra Bullock isn't as far off in concept as it seems. Just because they aren't superheroes doesn't mean they can't hold a brand and previously held idea to be re-ignited in a new film.