Unfortunately, raising prices will not help.
Undesirables come from both sides of the income scale. People will find a way to go. I would bet there are some who put of paying the mortgage for their trip. Additionally, thinking that less people will attend at a higher cost price point has also proven incorrect.
Also, increasing prices I think will only add to the problem. If the park ticket is $50, and you miss the fireworks, you still had a good day, but at $200 a day, the sense of value of how the park is toured is greatly increased. At a high price, you want to maximize that cost with the value, and I think we past that point.
I believe Disney needs to 'sell out' the park each day. Not the phased closures due to capacity, I think the tickets should be sold similar to a sporting event, and attempt to redistribute the crowds to families that are more flexible. Instead of a phased closure at 60k people, only sell 40k work of admission each day.