You just proved Whiskey Tango correct that with fans its a lose-lose situation.
If you use him too much --> "Thor was an add for the Avengers"
too little --> "He didnt have enough time"
I'm greatful that we got to see him even if he did nothing. It helps me feel like this is the Marvel Universe and not just Thor in a real life scenario like say Nolan's movies are doing. I like to feel that the world is full of superheroes, freaks, aliens, etc.
In a similar way i'd love to see Jack Ryder instead of random reporter number 3, Harley Quinzel being a doctor in Akrham even if she's not gonna be Harley Quinn yet, and so on. Its the same as seeing the Lizard Doctor guy in Spiderman 2 even if he didnt become the Lizard.
As for Black Widow and Shield's extended roles in IM2, i loved them too. Anyone who's read an Ironman comic book knows that those characters are IM's Alfred, Gordon and Fox. In fact Shield appears in IM comics 10 times more often than in Thor ones. So the problem was that IM2 didnt handle its subplots as well as it could have. I think that Shield had to be in both movies, serving as the overseer of superheroes.
I digressed. My point is that we shouldnt be afraid of other superheroes appearing, or making cameos in the films. They wont hurt if handled right.