I know you've already made your exchange, but here's a little more information. Our son went to the Badlands last year with his Scout troop during the third week of June. The weather during the day was warm - definitely didn't need a jacket. However, at night, most of the boys were cold. They were tenting it, and brought only a light, fleece sleeping back. If they had to do it again, they would have packed much warmer clothes for the night. Just a bit of a warning about the weather at night.
A few years ago, I had tried, for a long time, to exchange in to this resort during the summer months using an Embassy Grand Beach. I never saw anything pop up. I'm glad you're able to make this exchange. You'll have no problem finding enough to do for a week.
Also, if you're able to, could you take a few digital photos of the timeshare and submit them to TUG? It would be wonderful to have more info about this resort online.