I don't think
Disneyland Park really needs anything new right now. Perhaps a ride that's not a thrill ride, but still enjoyable, like Buzz Lightyear in the MK in WDW or Spaceship Earth in Epcot.
The Studios should be their focus. Right now, there's just not enough there. I couldn't imagine buying a one day-one park ticket and spending 40 Euro to go there (at least they have park hoppers now).
I think the Studios needs something like the Great Movie Ride at MGM. Just something about movies in general. It might be difficult due to the language barrier, but I think they good design it so that each car narrates in one or two languages, as it is with the Studios tram tour. I think they tried to do something like this with Cinemagique, but it's not the same.
I like the idea of a Tower of Terror, but maybe they could do the same idea with a new concept (i.e. a free-fall ride without the Twilight Zone theme). I can't imagine that the Twilight Zone was ever terribly popular in Europe. Too bad they already put in Star Tours in the Disneyland Park. That would have been good in the Studios.
I think a 3D show might be nice. Something like Mickey's Philharmagic in the MK...but that might be too much like Animagique, I guess, and that's one show they should NOT mess with!