I definitely think its worth it once. The cottage, pre-show stuff really is well-done. Yes - it's about the kids - but they need some adult volunteers for the story time, too. I wouldn't wait over 15 minutes, though.
It does depend on your strategy for the day, though. It will take up some time at rope drop time. Our plan is to do rope drop and old FP first thing, and we booked our FP+ for late afternoon - including ETWB.