We tried a lot of neat stuff on our last 2 trips, courtesy of the Gold and Platinum Plans. Some we'd pay for separately and do again, some we wouldn't.
We liked the Illuminations Cruise but we probably wouldn't pay for it.
We loved Cirque and would definitely pay for that again.
We loved Victoria and Albert's (although that depends on your in-laws. My mom would love it, my dad would hate it). We would pay for this again.
We tried a lot of the backstage tours and the highlights for us were Dolphins-in-Depth and Aqua Seas, but we probably wouldn't pay to do these again - they took the plan that included these away

If you love animals Backstage Safari is really neat too.
We tried the watermice and horsebackriding, they were fun, but we wouldn't pay for these.
We also enjoyed parasailing, but there's no way we'd pay the extra $ to do this if it wasn't included in a plan!
I'd also emailed Gifts of a Lifetime before our last trip and was presented with a really neat scavenger hunt idea, but at the time we didn't have the $ for it. so that would also be something very different.
HTH and have fun coming up with ideas
