We attended last summer. Louisville is actually a fun place to visit. We visited the Louisville Slugger museum and there are very nice restaurants in town. Also worth a visit are one of the many bourbon distilleries in Louisville, quite interesting!
There were quite a few parents there, but
@emwvmi01 is correct in that there is no expectation for parents to attend. We took a few of our DS's buddies to lunch with us since their parents did not attend. It was really fun to see the rapport that had been built between his platoon members. The bond of friendship was palpable.
If you do go, I would pass on the Parent's Day Feather and Quill dinner at Ft. Knox. The food was okay, but there really was no reason to attend it. It was just a buffet dinner with no speakers, presentations or anything. We got to meet a few other cadets and their parents, but it was kind of dull. In retrospect, we would have preferred to go out to one of the other local eateries in the immediate area. (You won't have time to go into Louisville and have your cadet back in time).
Bottom line, if you can afford the trip, it can be a lot of fun, and your cadet will likely appreciate seeing you after a month of bugs, humidity, rain, and mud. If not, it is okay as he or she won't be alone.