We did a rehearsal dinner at Shipwreck Beach- it was wonderful. At first, I was going to invite everyone to the bbq on the beach and then head over to our Illuminations Dessert Party. However, once we started adding up everything, we had to make some cuts. We ended up having about 30 people for the beach bbq- we went VERY casual- I believe the Chip & Dale BBQ buffet menu (hamburgers, hotdogs, bbq chicken, beans, etc). I asked them to take the dessert off the menu and reduce the price since we were going to the dessert party afterwards. Of course, Disney worked with me on this. We also served just beer & wine (also cut some costs rather than all open bar). I did work with Disney florist to put some casual, not pricey centerpieces on and added hawaiian floral print tablecloths. It came out really great. The only thing you have to worry about is the weather. It started to rain towards the end so everyone ran under the trees. It was much better than raining on our wedding day! It is a wonderful, beautiful location and I'm pretty sure you can see the Epcot fireworks from the beach.
You can definitely ask your wedding planner to help with this- Marion planned everything and even added some extra bonuses we didn't ask for. Good luck!