Present value of that $11K is only $3K and included in the NPV number.I'd say VGF being $11,000 cheaper is pretty stark. Especially since VGF is typically more expensive to stay at!
The biggest factor in how much a buyer will save from DVC is the upfront purchase price. 2nd biggest factor is dues and dues inflation. 3rd is expiration.
This is something Disney exploits because they will tell buyers about long-term savings (without adjusting for the time-value of money) and years of vacations, while they make bank on your $30K buy-in. They want buyers to be distracted by the long expiration to forget how much money they're spending.