Although you may be able to see all the attractions for cheaper by buying the discovery pass on its own, you wouldn’t get to the front of the lines at Cave of the Winds or the informative tour and recommendations on how to spend your time and where to eat. Tour guide was also happy to take group photos. For us it was worth the extra.
As for the Discovery Pass, the Caves of the Winds and Maid of the Mist are the big attractions. I could take or leave the others, but since they were included we went. The aquarium is small, but the seals were neat. The theater was a nice way to cool off and learn a little history.
We did the 9:00 tour and had plenty of time to see everything and eat at Top of the Falls restaurant for lunch.