I think Disney has more "hits" than "misses", but they're not infallible. Remember, these are the people who brought us The Lone Ranger and caused John Carter to die at the box office because of their less-than-brilliant marketing/promotion plan. You'd think with a property like Star Wars that they would want to make damn sure it's handled properly, but with this much money at stake The Mouse's greed might get the better of them.
Aside from the possibility that Episode VII might turn out to be a not-so-good movie, my concern is that between Episodes VII, VIII, IX, however many standalone movies they're planning, and all of the promotion/marketing/merchandising, they're going to over-saturate the market and make people sick and tired of suddenly seeing Star Wars everywhere.