I agree. The Star Wars universe is pretty vast and has, like you stated, 40 years of a fan base already. Potter? It's really up to JK Rowling. If she truly holds her ground and Harry and the Hogwarts gang are 'done', then so is that universe. It's sort of like LOTR and Tolkien. That could have been an amazing and even more immersive environment than HP....right up there with Star Wars had the professor's literary executors allowed for sequels, spin-offs, etc. Imagine what could have been built and experienced for theme parks!
But, back to Potterdom. I can't argue that what exists is wonderful and it will always have fans. It will undoubtedly also get a good deal of new ones, but without new stories and especially movies there's only so much you can do. My gut feeling is that since 'money talks', eventually she'll write new books and there will be new stories, characters etc. to use.
Still wishing for a Middle Earth though...