Batman wrote:I dunno. The hammer at the end of 2 was a fun infodump, and The Avengers certainly worked, but I want Iron Man movies to be about Iron Man. What would The Other Guy or Banner being in the movie add to the movie? We already know they're part of the universe.
Just have Banner stop by, give Cap a call, you don't need to spend more than thirty seconds on them and these are movies to make nerds happy and make tons of money via making nerds happy. Why not make them happy when it costs so little and makes sense from an in universe perspective. Not to mention it starts letting you comb other movies for supporting characters.
If Tony is thinking on a problem related to the suit (As part of every Iron Man movie is the new suit building) and he goes down to his workshop works on his suit, decides to hit up his Avengers headquarters and bounces an idea or two off Banner, gets a good suggestion in return. No need to introduce generic scientist number 5 when we can have Bruce Banner play that part. It feeds back into that interconnecting framework.
Have you forgot one of the classic comic book tricks? Not putting everything in the same issue? Want to know about X, well check out Y issue of Z hero to find out what happened. You can of course abuse this to a large amount, but it's also possible to make people want to give Y a chance. So you have Bruce in there to for thirty seconds to lead into the next bit, maybe he gets a full minute in Thor 2 then it all leads into Hulk ...whatever number. You don't do it for all of them it won't work well and Banner is the natural pick besides Rogers for someone to lead into their movie even as they lead into Avengers 2. Remember these movies are being made with the idea of not only getting to you watch them but also getting you into the next Avengers movie, so why not lead into not just the Avengers but Thor 2 or whatever movie of choice.
*Edit
And you can do this all naturally by establishing that yes Banner is working for Stark now, Hulk never has to show up, but remember the targeted demographic of these movies. Even tiny bit of of character X produces lots of internet buzz which translates into extra free advertisement. There are a dozen reasons why you include a short spot from one of the other Avengers even if they don't get within a 100 miles of the stompy robot fights.