I don't have luck finding SW stuff at Goodwill or Yardsales either... I dream of that same dream, but no luck for me. I think it's more miss than hit generally.
Lot more miss than hit, and if there's a craigslist garage sale ad that mention Star Wars product specifically, you better be the first person there!
Some summer weekends I could hit 30+ sales and not find anything toy wise worthwhile.
Just buying some junk lots off ebay would be more economical, given the cost of gasoline (as well as the hours of your weekend wasted looking at ceramic frogs, holiday decorations, fast food toys, romance novels, religious materials, VCR tapes and all the other dreck that is commonly found at yard sales).
But then I wouldn't have my sub-collection of incomplete ROTS Jedi starfighters and handless action figures!