You won't have a good view for MSEP. At best, you'll see the tops of the floats and it's quite a distance away. Robo has some good maps on here - search "Dessert Party" and they should come up. You'll be able to hear the music, but that's really about all of the experience you'll get. Tomorrowland Terrace is a little to the left (stage left or to your right as you walk down Main Street), so you're not going to be head on. You can see the castle and fireworks just fine - almost unobstructed, there a few trees around, but they won't hinder your experience. The cool part is that Tinkerbell will fly right over you and land on the roof of the restaurant, so make sure you have your camera ready for that!
When are you going in Decmber? If it's closer to Christmas, there may be a chance of a second MSEP getting added to the schedule. If there is, you can do both without a problem. If there's only one MSEP scheduled, you really don't have a whole lot of time to go from the Hub to Tomorrowland Terrace. The only thing you can keep in mind is that there are reserved seats for the Dessert Party, it's not first come first serve. However, once Wishes starts, they will stop serving desserts and by the time Wishes is over, they will have finished cleaning up or at the very least started to dismantle the buffet.
In my opinion (take this as you wish), I would skip trying to see MSEP from the Hub, sit back and enjoy what you can from the Dessert Party. Not having to fight your way to find a spot for Wishes was a big plus for us. Also, the desserts were plentiful and assorted - we really enjoyed them! I would suggest booking (reservations open up about 45 days in advance) and if you would rather see MSEP and they don't add a second showing, you can cancel with 48 hours advance notice and get a full refund. You are able to book online or via Dining Reservations, but know that you have to pre-pay for this event.
Whatever you decide, hope you have a magical time!
