Unless you are avid hikers, the Badlands is an interesting bit of geology to see mostly from your a/c vehicle :) but it is worth the time to drive through it. The campground at the visitor center has elec, water and dump and showers, but there is no shade and it will be hot. The cafe is good with indian tacos big enough for two people.
The town of Wall and Wall Drug is a campy attraction but it's worth the time, too.
And staying over there is not a bad idea.
There is a National park Museum of the Minuteman system of defense on the other end of the park and it is interesting, too. plus there is a missile site you can drive out and do your own walk around with a recording on a phone.. free.