Love it out there! Personally I wouldn't plan too much. Planning ruins adventure. .
We didn't go to the museum. I've probably got 100k motorcycle miles under my belt. I just think the "culture" of bike rallies is very banal and was destructive to what I am sure was once a cute town.
Still is go back for another visit this summer if I could.
One thing you might want to see about planning is a night blast at crazy horse. They turn it into a fireworks display which is supposedly incredible. We missed it by a week