I just got back from a couple of days in South Dakota, hunting for vintage clothing for my store, Vintage Haberdashers, and seeing the sights. SoDak is a land of stunning natural beauty and wonderfully old fashioned tourist traps. These roadside destinations were populated by an amazing array of characters, re-purposed department store mannequins, aging wax figures, secondhand animatronics, and statuary.
Wall Drug
510 Main St, Wall, SD 57790
Pioneer Auto Museum
503 5th St, Murdo, SD 57559
1880 Town
Interstate 90, Midland, SD 57552
Diner Hunter 
Very cool. Were you anywhere along the Mickelson Trail? I’ve enjoyed that area for all of the attractions you note a number of times.