In all of our trips to WDW, we've only seen Star Wars characters just walking around 1 time (unless it was part of the Stars & Motorcars parade where you'll also see R2D2.) We've seen Luke, Leia, Chewie, Darth Vader, the Emperor & his red guards, stormtroopers, Bith (musicians from the cantina scene), and an Ewok. Vader and the stormtroopers were just pacing around by Star Tours. The Vader wasn't very good and wasn't accomodating when trying to get a picture. The stormtroopers on the other hand hammed it up very well and would grab you like they were making an arrest. The Emperor and his guards didn't stop for pictures, but would parade themselves between Star Tours and Sci-Fi. Luke and Leia were in the shaded area between Star Tours and Sci-Fi signing autographs and posing for pictures. Chewie and the Ewok did the same thing and they were next to the speeder bike.
When we were there in May 2002, we ran into the same problem as you. We booked our trip planning on attending 2 Star Wars weekends, only to find out that they canceled them that year due to Celebration 2. When we went back in May 2003, our APs expired early May, so we missed the weekends by 2 weeks.
We're headed to Celebration 3 in Indianapolis in just 2 short weeks and plan to hit a Star Wars Weekend in late May 2006.