My family feels that Splash Mountain goes a lot faster during the evening, when it's dark outside. I think that could be perception due to the dark.
I can not ride the Sun Wheel at night, it's way too freaky, I feel so afraid of heights then. Maybe I'll try it again, to conquer the fear.... I went once for the first time in the dark, and was surprised to learn then that I have (apparently) a certain fear of heights. (I could go on California Screamin' and not feel so nervous, and in fact, loved that ride.) Anyway, the next time (in a year) we went on the Sunwheel ride in the day time - I had decided I would try to ride it in the day to see how I felt, and although I felt squeamish still (we were always on the non-swinging gondolas, BTW), it was far better than at night. I think that the dark does play with your head a bit!
My DH pointed out to me how much better you can see on the PotC ride at night - because you are used to walking around in the dark in the evening, the cones in your eyes have already gotten accustomed to the dark, so are then prepared for the dark rides more easily. At least, that's the non-scientific reasoning my DH and I came up with. But try it, seriously, notice how little you can see into corners and nooks on the PotC ride during the day, and then at night it just all jumps out at you!