Based on my experience at Knoebels, camping on-site at the amusement park has some benefits that may not be immediately obvious. Cooking your own food for lunch and dinner (and not paying park prices for food) can save a decent bit of money, partly offsetting the pricy campground rates. Besides that, having a home base available to change, to take a siesta, to leave the camera in rather than carrying it around all the time, etc. is very convenient, as is not having to worry about battling traffic when leaving at night. You can also factor in not having to pay for parking if you'd be driving from another campground to the park.
On the other hand, $100+ per night is indeed spendy; there's no way around that. I myself would probably be tempted to stay at Lightouse Point for two nights (around the day at the park) and move to another campground for the third most likely.
