We've eaten at the clambake at CMC on both of our last trips. I don't eat seafood but DH loves it and this is his favorite meal. We are going again this May and he is insisting we eat there again. As a non-seafood eater, I love the buffet as well. I remember the ribs to be delicious both times. DH ate almost all the seafood - clams, mussels, shrimp, fish, etc. The clams are served steamed in a big pile and then the butter is on the side. Even as a non-seafood eater, this is one buffet that I usually have overeaten at as all of the food is good and there is a lot to pick from, a nice salad bar part and then all of the main food, breads, etc. I am usually so stuffed that I barely have room to taste the desserts. Our daughter was 5 on the first trip and then 8 on the last trip and she loved the buffet as well. They have the usual kids buffet and then of course the kids can eat any of the food from the regular buffet as well.
We have always felt that the price is a great value especially if you are a seafood eater. It's only $26.99 for adults and $12.99 for kids. Compared to the prices at other dinner buffets at Disney that don't have all the seafood, it's a great price. We stayed at the Poly on our last trip and we did the clambake on our Epcot day so we just left the park through the back entrance near England in the World Showcase and then it's about a 5 minute walk down the path to the Beach Club. If you are going there directly from the Poly, I guess you would take the monorail from the TTC to Epcot but then you will have to walk all the way to the back to exit toward the Beach Club. I would highly suggest coordinating the meal with spending time at Epcot as it will be a lot of time to get there just for the meal itself.