Re: Characters you'd like to see in future Avengers movies?
You are assuming that Disney/Marvel don't already have a deal in place. I think they altered their relationship last November when they purchased the merchandising for TASM. Iger was quoted as saying that Sony purchased from Marvel their involvment in TASM films. Now that is fairly vague, but I think they may have made provisions for this type of cooperation. Maybe not.
My perspective is a little different though. I'd just like to see TASM as part of the MCU, not necessarily Spider-Man in Avengers, though I would be OK with a cameo. I don't think they would make this type of moved based on some sort of mathematical equation, thinking adding TASM to the MCU will equal an additional X millions of dollars. They'd do it based on fan anticipation and whether or not Spidey would bring something to story. Would the character make the MCU richer or the stories more fun and exciting? Those are the drivers for something like this.