Went to cedar point a couple of years ago and stayed at the CG inside the park.
Cedar Point has a great CG right there I would not stay anywhere else.
We did a day trip to Kelly's Island. Very nice. While I considered taking the RV across on the Ferry I could not justify the cost for the amount of time we planned to be there. If I were local to the area I would certainly stay at Kelly's Island. However I had a lot of exploring to do and opted not to spend too many days at KI.