As someone who started with a Class C and is now the owner of a 40' Class A, I agree that going with the Class A is a good choice. We only kept the Class C a year and traded it in. My husband, who has his commercial license and can likewise drive anything, could not believe the difference in the handling and stability of the Class A over the Class C. It makes a huge difference on long drives. I'm told the diesel engines hold-up better than the gas engines, so that was another deciding factor when making upgrade to the Class A. I agree with one of the previous posts that the floor plan makes a difference and although I'm not sure of the ages of your children, I know mine would have outgrown the sleeping area on the Class C quickly.
I would make one recommendation, however, which is that the better RVs are often more expensive because they are built better. If you plan on keeping the RV for a long time, it may be worth putting in a few more dollars now and ensuring that you get a quality product.
We also own a DVC membership - purchased before we decided to purchase the RV - and we split our stay between a villa and the Fort every time we go now. We arrive and spend a few days at the Fort and then move to the villa. It's the best of both worlds! Good Luck!