While
DVC revenue is very important to Disney, we still represent a very small portion of the daily guests at WDW.
With all DVC resort rooms booked and at full occupancy (4/4/8/12), the total DVC members at WDW would be around 15,000. When you factor in vacancies, rooms occupied by cash guests, rooms out of service for maintenance and, of course, rooms not at full occupancy, it's probably closer to 10,000 on any given day.
Spread that out over 4 theme parks, 2 water parks and people who have non-park days (Sea World, US, IOA, DTD, sitting by the pool, etc.), DVC members probably represent less than 5% of guests in a part at any given time.
As a whole, I think it would take a small miracle for Disney execs to ever be sold on a new theme park. They would probably have to stumble across some perceived "can't miss" idea that could not be integrated into a current park.
The problem is that opening a new park adds tens-of-thousands of dollars in daily expenses before you even get to a single ride. You've got to staff for security, parking lot attendants, ticket sellers and takers, park management, custodial, gift shop CMs, dining CMs, and so on.
And one of the lessons that Disney learned with AK is that adding another destination didn't necessarily convince people to add days onto their trip. In other words, most families who averaged 7-day trips before AK opened still took 7-day trips after AK. As such, the park itself didn't necessarily generate any additional revenue--it just moved the revenue from another park. Instead of spending 2 days at MGM, that family would spend 1 day at MGM and 1 day at AK. So, effectively the family is still spending the same amount of money, yet Disney is on the hook for all of the overhead expenses associated with running 4 theme parks rather than 3.
Personally I'd much rather see them add 2 or 3 great new rides to MGM and AK. Give me a reason to spend more time in each of those parks rather than wasting my time trudging over to a new destination.