I don't know if Episode VII will do Avengers type opening weekend numbers. The prequels left a sour taste in the mouth of the casual Star Wars fan. The only reason TPM made the most money was because it was the first Star Wars film in 16 years. The poor story certainly hurt the box office of AOTC and the poor story of AOTC hurt the box office of ROTS, which was easily the best of the three prequels.
The saving grace for Episode VII will be signing the big three to appear in the film. I think that will get people who were turned off by the prequels somewhat excited. However, you are going to get the "they are too old" crowd. The story will really be a key in all this. Disney cannot afford to have a boring trade dispute/political story line. There will need to be an enemy that is a credible threat to the Jedi and a lot more action than we saw in TPM.
When new movies were announced in the 90's, I really wanted them to make the sequel trilogy back then. At that point, the major stars were not "too old". Ford has always said he wouldn't play Solo again, but I bet Lucas could have at least got him to cameo for a death scene. The other reason was so that nine episodes would have actually been made. At that point, I never though Episodes VII through IX would be a certainty if Episodes I through III were completed. Until the Disney sale, that was the road Lucas went down with his revisionist "I only intended to make six movies" statement.