MGM is my least favorite park, so I am also a little biased (just in the other direction!).
We went January, 2007 with DD6 and DD2. We are going again this January with DD7 and DD3.
My 6 year old was frightened on the Great Movie Ride, so I would skip that. There are actually signs outside the attraction "this attraction may frighten small children". I didn't remember anything being that intense and didn't take the sign seriously. Take the sign seriously.
DD2 at the time seemed to like Playhouse Disney, but it isn't something that she remembers. DD6 at the time liked the Muppets (and I love the Muppets). We also saw The Little Mermaid, but I don't think that my kids are big "watch a show" fans. And they are girls that will sit still for many things. They sat still, but just didn't seem interested.
I was going to skip MGM on our next trip, but DH said that we HAD to go to see the High School Musical show. DD7 (she was 6 last time) is nuts about HSM. That might be a reason that you go to MGM (since you have an 8 yo and a 7 yo). DH also talked me into the Playhouse Disney charcter meal. Next time that we go, they will probably have outgrown Playhouse Disney.
We missed Beauty and the Beast last time (I've actually never seen B and the B show), so I would like to see that, too. It can be difficult to get a lot of shows in because of the timing (esp. if you plan on the nap in the afternoon). DD7 might ride Rock 'n Roller Coaster (I'm crossing my fingers). And I really want to see the Walt - One Man's Dream attraction. And maybe the Animation Tour.
Our trip is a week long - any shorter, and I would skip MGM. Like I said, it is my least favorite park.
Have a great trip!