Timkin,
If you search the many threads on these boards about Cirque you'll be hard pressed to find anyone who had anything bad to say about this show. I think it's fabulous and worth every penny. 7 and 9 is not too young to appreciate the show. And the action always keeps going, so they will not get bored. If you can afford the $228 I say go and enjoy. (Of course if you don't have it in your budget and you were thinking of substituting a park day for this I say don't do it).
As for BB, Cirque and PI, it can easily be done in one day. However, are you planning on taking your children to PI? There is not much there for a 7 and 9 year old. Cirque is at DTD, right next to PI, so if you wanted to do PI w/out the kids you would have to take them back to the resort after Cirque and then go back to DTD for PI.