We have camped at FW almost every winter for the last nine years and just returned from our first summer trip. And were coming back this winter.
In my opinion there are many reasons to stay on-site.
1) In the winter the parks close earlier during the week We always come back to the camp site, cook a hearty winter dinner, go to the camp-fire and movie, or watch the water light parade, or have hot chocolate at the trails end or just relax at our site playing board games and cards.
2) In the summer we come back from the parks at mid-day, eat a light lunch, get cool, walk the dog, take naps and venture back to the parks again in the early evening.
3) We defiantly take advantage of the extra hours for resort guests only. Our older teenagers like to get up early and beat us to the park to get their fast passes or even be 3rd in line for the rockin roller coaster.
4) With 4 kids spanning all ages we like to split up and the teenagers like this freedom and meet back at the campsite or the parks during the day.
5) You dont have the stress of getting up, getting in the car and making sure everyone is on the same schedule. It was just a less stressful way to spend the day.
We have camped off-site, and there are some nice campgrounds close by. But it just feels more like a vacation when you stay at FW.
