Exactly what we did. Drove to Hershey on Thursday, did Chocolate World that afternoon, took advantage of the “sneak peek” that allows you to enter park free after 8pm if you have a ticket you plan on using next day, went back to the park (and Chocolate World) on Friday, then drove the ~45 minutes to Gettysburg for Saturday/Sunday.
HersheyPark was nice, but as a family, we enjoyed Chocolate World and it’s offerings more, to be honest. We are equidistant from there and Cedar Point and while considered Cedar Point, decided on Hershey instead, mostly because of Gettysburg.
That was a fun long weekend but would never replace a planned Disney trip. We ended up at Disney for a day anyway this year when the weather was crappy in Clearwater. Perfect weather at Disney though.