OP is doing a lot of jumping around, butttt it may be due to reservations and available openings, and that reunion.
Note, I have been to a number of the locations I mention, though not all of them, however my next visit will take in more of them that I missed the first time.
Instead of a discussion about the qualities of Wall Drug and Rushmore, here are some places that may be of interest in your visit to the Black Hills region.
1880's steam train, Hill City to Keystone and back
https://www.1880train.com/As a kid I loved to go to the local museum. I still enjoy museums and many others do too.
The Journey Museum in Rapid City, huge and very well presented.
https://www.journeymuseum.org/visitAlso in Hill City, South Dakota Rail Road Museum,
https://www.sdrm.shop/The Civilian Conservation Corp Museum of South Dakota, Hill City.
https://www.southdakotaccc.org/Wind Cave National Park,
https://www.nps.gov/wica/index.htmThe Black Hills is not a large area, take a ride to the south side to Hot Springs and visit the Mammoth Site,
https://www.mammothsite.org/If going to or from the Black Hills from the south, stop when you get to Chadron NE and go east on US 20 for three or four miles to the Museum of the Fur Trade. Might sound hokey but it is an excellent museum with many rooms of displays of original Native American and Fur Trader artifacts,
https://www.furtrade.org/Some people do not like the Crazy Horse memorial but the museum is worth the visit,
https://crazyhorsememorial.org/There are nighttime activities at both Devils Tower, and Rushmore that are pretty good. I did not do either but many people rave about them.
Into airplanes and such, visit the South Dakota Air and Space Museum on the grounds of Ellsworth AFB, just east of Rapid City,
https://www.sdairandspacemuseum.com/On the way to Devils Tower stop at exit 199 at the Wyoming Welcome Station, it has very nice displays which are exceptional for a welcome station. Just up the frontage road from the welcome station about a half mile is the Vore Buffalo Jump.
https://vorebuffalojump.org/ which is a sink hole that has been excavated that the early plains Indians used as a place to stampede buffalo into to kill and butcher them. Interesting if you are into the Native American history of the region.
Entrance to Rushmore is free, but Parking is $10 to the concessionaire (half price for seniors), which I assume helps pay for the parking garage. The Badlands is $20 and Wind Cave is free to enter the NP and has fees for the tours. Devils Tower is $25. If you plan to hit enough Federal Parks that charge fees, get the $80 annual pass and it will pay for itself. If you are 62 or over then you should already have the Senior pass which is $80 once in a lifetime. If you don't have the annual pass it can be purchased at virtually any National Park entrance, Army Corp of Engineer location, etc, but get it ahead of time if you can.
https://store.usgs.gov/pass/index.htmlHere is a complete list of places you can purchase the passes, this is a 45 page PDF file.
https://store.usgs.gov/s3fs-public/PassIssuanceList.pdfSpearfish City Campground is very convenient to Devils Tower, the Spearfish Canyon Scenic Byway, and much of the Blackhills, especially the north half. It has full hook ups, and is adjacent to the previously mentioned fish hatchery (which reminds me more of a Japanese garden than a fish hatchery). The campground is open year 'round but there is no water, restrooms, etc after Oct 1st.
If you were to go there, follow the website instructions for getting to the campground as the GPS systems want to take you over a blocked off road with no means of turning around. The campground is easily accessed thru the town.
https://www.cityofspearfish.com/185/Campgroundhttps://www.cityofspearfish.com/Facilities/Facility/Details/Spearfish-City-Campground-1Be sure and drive the Spearfish Canyon Scenic Highway/Byway, and stop at some of the pullouts and admire the area.
In Spearfish you will find the
https://www.westernheritagecenter.com/ which you may find interesting.
There is a hike/bike trail called the Mickelson Trail
https://gfp.sd.gov/parks/detail/george-s--mickelson-trail/ which is converted from an old railroad line that travels thru the Black Hills, you may be interested in doing parts of it.
There are a couple of web sites that will help you locate attractions in the Black Hills area. You will find the printed maps all over, virtually every place you stop will have a tear off pad of them (they are large) and as cell phone service can be spotty, I highly suggest having a printed map in hand.
https://www.blackhillsbadlands.com/mapshttps://www.blackhillsvacations.com/plan-your-visit/black-hills-mapsYou will find these web sites helpful
https://www.blackhillsbadlands.com/https://www.blackhillsvacations.com/https://blackhillsvisitor.com/Charles
'03 Ram 2500 CTD, 5.9HO six speed, PacBrake Exh Brake, std cab, long bed, Leer top and 2008 Bigfoot 25B21RB.. previously (both gone) 2008 Thor/Dutchman Freedom Spirit 180 & 2007 Winnebago View 23H Motorhome.