I could spend a week just watching the water.
Clifton Hill is a midway at a carnival - go there knowing that and expecting that and you won't be disappointed.
Over 100 years ago, a female journalist came to see Niagara Falls. After a few days of running around doing everything, she went back to Europe and wrote that it was all a waste of time. But she kept hearing people ooh and aah over it, so she decided to try it again. This time, she found a nice quiet spot and just watched the water go over the edge. When she went back to Europe, she wrote that it was a must see and an amazing place.
What I learned from her experience (and I have seen repeated in others all the time) is that you really need to just sit and watch the water for a while to "get it". If you just take a quick look or run around trying to do everything in a short time, you miss it. The awe is in watching the deceivingly peaceful flow of water going over that edge and realizing how much power it really has. There is something very hypnotic about it (many people who were rescued before going over the falls have said they just felt an urge or a need to go in the water and feel it around their feet).
So, plan what activities you'll enjoy and then spend time just experiencing it. I usually estimate 2 activities per day - so if there are 6 activities I want to do, i'll spend 3 days there. That always gives me enough time to just experience the location and/or to add in something I didn't expect. If you try to fit those 6 activities in one or two days, you'll miss so much.
Also, check out T.W. Kriner's books In The Mad Mad Water and Journeys To The Brink of Doom. Lots of true stories of people and animals who have gone over the Falls throughout the years.