Depends on your preferences. What's worth seeing for me is the Badlands landscape, prairie wildlife, and geology. Mount Rushmore and Crazy Horse monuments to me are graffiti, but those are what my children want to take their children to see.
Historical reconstructions and living history museums, I can go either way. Some appeal to the anthropologist and historian in me, others go to far with the Hollywood-style reenactment of things that didn't actually happen outside the movies, but that appeals to other people, else they wouldn't be making money doing the show.
Sturgis is about an annual event, rather than the place itself. If you are into biker gatherings, it might be worth going at that time, but I wouldn't be taking children. As a biker gathering, I think Sturgis is better than Myrtle Beach, but doesn't come close to Daytona. There are many other gatherings, different times and different places, certainly haven't been to them all.
