Sadako said:
Look at the CG effects used in Jurassic Park compared with the CG used in AotC, ten years later.
In Jurassic Park, they had to make the CG dinosaurs look indistinguishable from the full scale models and animatronics that were used in close-ups, and the effects still stand up today. In AotC, they used CG for everything--the aliens, the vehicles, the sets, everything, and the effects haven't aged particularly well (compared to films that are twice as old). If they had used animatronics or actors in make-up, it would have given the CG artists at ILM something to shoot towards in their rendering, something real to match.
This featurette is particularly illuminating, given that they're talking in the early 90's about effects technology that moviegoers take for granted now. (Also, physical models of the Falcon against bluescreens in '77.)
It's ironic that a film that used a balanced mix of CG and physical effects is the very film that convinced Lucas that CGI had advanced enough so that an entire film environment could be created with it.