I disagree somewhat. Yes, lots of prequels, sequels spin-offs are less good than the original, but some work. How about Buffy-Angel, for example? Or LOTR after The Hobbit, definately a sequel! If it's done good and in the same line as the original, and with the same high standard qualitywise, then it can't do no harm, can it?
By the way:
JK Rowling to pen Eighth Harry Potter Book? | /Film