Monkeys, chimps, baboons, gorillas, apes, gibbons...there are so many species they could put in. Have them swinging from the trees, howling, playing, etc. A gorillas in the mist type of thing might be kind of cool (ie. a charging gorilla stops near the shore and the tour guide insists everyone look down to indicate the gorilla is dominant. It then moves away). Of course, as I mentioned before, I'm not into changing it into something frightening, so this might not work.
I've always thought the veldt idea should be expanded on, too - more animals in a larger area, perhaps on both sides of the boat.
But guys, don't downplay your Jungle Cruise. As I also mentioned before, you've got a temple Disneyland doesn't have, as well as a downed airplane, and couple other things I'm forgetting right now. Honestly, I thought Disney World's put Disneyland's to shame. I wasn't really all that impressed by the pirahna part, and the ape scene is okay...but it's not all that different from the camp scene you've already got. There's just an ape shooting a gun and hitting a box of explosives. They're nice and all, but I think your differences make it a better (and longer) Cruise.