Rumor is that this is just a very extensive cleaning. It was initially rumored that they were going to change the old entrance ramp to be the new exit ramp, and vice-versa for the old exit ramp. I believe that that's not a go anymore.
I believe that the roof contained asbestos and that they had to remove a lot of that. Plus, several of the dolls simply weren't working and had to be fixed. The roof was missing pieces in places and the whole ride needed just a general 'dusting' and cleaning.' They're also making the soundtrack a little clearer.
There's still a rumor going around that a new scene will be added, but that's just a rumor.
The last time I went on it (last summer) I noticed that the roof was missing pieces and it all kind of looked dirty. I think it's great that they're doing this, because even though everyone in our family makes fun of it, we still get a kick out of it.
RyMickey