Christopher Plummer is actually really good in this movie. Sure, he doesn't even TRY, but he imbues gallons of emotion into even the most stonefaced stare.
The robot on the other hand .. painful.
The Onion's AV Club did an interview w/Plummer a while back where they threw out various titles from his back catalog at him, so he could comment on each. When they got to "StarCrash," he said the main reason he did the movie was to get a free trip to Rome.