Good question. I’m often with my family for some of those days. I’m not knocking anyone who isn’t, obviously, but I don’t have a good sample.
At my local casinos, action definitely picks up during March Madness. I often go during part/tail end of New Year’s, and it’s a zoo then. I’d have to think it would be packed during the Super Bowl, though people are also going to be watching the game (I’m sure hitting the slots hard before and after).
I’d probably lump many of those “day off from work” days together, as I’d be surprised if there was a noticeable spike with one over another.
I’ve heard from slot attendants that it’s busy on Christmas (but later in the day, not the morning or afternoon), and this thread implies as much too. That thread also mentions Thanksgiving being not all that busy at the casinos. I’d add Valentine’s Day as a “busy day” to the list as well.