Having a few extra superheroes wont increase revenue by that much. Its like when I book a concert. If I have My Chemical Romance on the bill, theres no reason for me to blow money on say, Aiden, since the vast majority of their fans will already be coming out to see MCR. It only really helps revenue if I add so many freaking bands that it becomes an event, like Warped Tour. So, since Iron Man, Hulk, Captain America etc all share the same fans, you shouldnt expect any significant revenue increase unless its seen as a major event in movie history. We all know it is, but will the general audience? Marvel is gambling that they will, and it is possible. It would be a much bigger deal if Spider-Man and X-Men were involved, but that aint happening. The Avengers movie is likely to outperform all of the individual movies, but not by bucketloads. If you aren't interested in Iron Man, you probably didnt see Hulk either, and arent likely to care if they are in a movie together.