Good Point Lisa but what if you took that iniital cost of 15000 and invested it lets say even in a conservative investment arent we jsut about breaking even. I luv the Dis but I cant see Disney doing anything that is gonna save the consumer money and make them lose money over the long run. Their resorts were full before they built DVC. All they had to do was add on the BC and it would have sold out as well.

To me it seems as if they just got people to pay for a hotel that will one day be Disney's 100 percent. If it werent for the maintenance fee and there increases I would be sold on it.
There are many ways to look at it. Don't forget to factor in taking money out of that conservative investment every year to pay for similar accommodations at WDW, making up the difference in what you would have paid in dues, and what shortfall there is in the ROI you received on the investment that goes toward paying for the regular WDW room.
Simple Example, similar to what MtmMan posted.
Suppose you want to stay 5 nights in a WDW moderate, and compare it to 5 nights at BCV.
BCV mid season would be 65 points, so say you purchase a resale contract for 65 points and pay $6200. Your annual dues will start at about $4.50/point, or about $293 out of pocket. Next year dues go up 4%, so it will be about $304 out of pocket. Adjusting at 4% for 3 more years, you pay out of pocket $316, $329, $342. Your out of pocket for 5 years totals $1581.
Instead, you invest the $6200 and can manage 8% return. You elect to stay those same 5-nights in a Moderate, let's say at $180/night plus tax, or about $200/night. Year 1 you pay the DVC equivalent $293 out of pocket. You receive $496 interest on your $6200 investment, so your total is $789. Now to stay even with DVC, you have to withdraw $212 from your capital to have the total $1000 you need for the 5 nights.
Year 2, your now $5989 investment earns $479 in interest. Add the year 2 equivalent DVC dues out of pocket of $304, and you have a total of $783. The room however has gone up 4% so it's now $1040 for the 5 nights. You have to withdraw $257 from your account to make up the difference.
By year 12, your original investment of $6200 is completely gone, and you are paying the entire WDW moderate resort room out of pocket. After 20 years, you have paid a total of $14,910 (8,710+6200) for your 100 DVC nights, or you have paid $29,778 for your regular WDW hotel room. The major difference of course is that you still have DVC. Your $6200 DVC 'investment' is still paying off.
With DVC you still get new points every year for only the cost of the dues. Whereas your initial investment you used by not buying DVC is completely gone, and you will be paying regular WDW room rates.
The spreadsheet below shows these calculations. Of course this is the simplest version trying to keep an apples to apples comparison, and getting the best value for your DVC points (Studio, weekdays). You can change a lot of things such as having a 7-night DVC stay versus 7-nights in a WDW hotel. You would need to calculate the comparison based on your expected vacation travels.
Here's a spreadsheet showing the calculations:
One more thing. You have to pay taxes on your investment gains, so you don't really get that much back. This would make the difference between the two even greater. AND, a portion of the DVC dues you pay actually go to Property Taxes. You can deduct these from your income and actually save some more.