For the most part, our missed are ones we've done before, but choose to skip - like Stitch. Did that once years and years ago. There's no need for me EVER to do it again. I did Hall of Presidents even longer ago. Nope, don't need to do that one unless I'm really desperate for a place to hang out for a break.
The only attraction that is at least 2 years old that I know we haven't ever done is American Idol. I'm not motivated to go see that, as it's low on my priority list.
We haven't done the water parks though, so maybe that could count? We're doing them our next trip though.
Oooh, though of another - characters. We haven't been to a lot of the character spots. We don't want to wait in line for very long for characters so we see them when we see them. We always manage to see enough to make the kids happy. We focus on the rides/shows instead. And most dining - does that count as an attraction? Again, our focus is the rides/shows and table service would slow us down too much. Plus, table service would make it less of a vacation due to having to wrangle a child. At least we're down to just one child who couldn't handle table service though. Some day, perhaps!