Whilst I agree that the upside potential for the older resorts is probably less than the newer resorts it's difficult to price in the value of the ability to switch to other resorts at 7 months.
From reading these boards some members buy at the older resorts with no intention of staying at them. They take the view that it's a cheaper way to access the more expensive resorts at 7 months.
I don't think your reference to WB is that relevant to your argument. You could easily counter argue that WB investment theory says that
DVC is great value.
The biggest impact on DVC prices is longer term room rates at Disney resorts. You could argue that existing DVC prices are undervalued and should trade at a premium to existing room rates. You are locking in a price now, which based on previous history will rise much higher over the years.