Keep in mind that Disney 'owns' marvel. For the most part they'll let Marvel do what they do best, but now it means they can incorporate the colourful characters into their marketing plans without having to pay or get permission. Keep in mind that Disney owns a lot of other film companies that make more 'grown up' entertainment.
It'll be the same case for Star Wars and Lucasfilm. The quality of Star Wars will be less affected by the 'Disney' brand than it will be by the artists that are chosen to run it. Sure, it could end up being terrible, but that wouldn't be a change from what we've come to expect from the Prequels. Then again, now that Lucas has all but relinquished creative control this is the first time we'll actually have a CHANCE at getting a good Star Wars movie since ROTJ.
Disney being the recipient of the Box office profits won't be the reason for its success or failure, any more than it was for 'The Avengers'.