I think your missing something. Don't think about it as your
DVC will cover cruising. Think about them as separate transactions.
1) Buy DVC and pay annual dues
2) Sell your DVC points every year in exchange for cash (or credit)
3) Use the cash (or credit) and use it to pay for the cruise.
Example 1
Lets say you bought 400 Saratoga points direct @ 160.
400 x 160 = $64,000 purchase price
400 x 6.76 = $2,704 annual dues every year (then adjust for inflation)
If you use Disney's cruise swap program, they will give you about $8 per point worth of cruise credit.
400 x 8 = $3,200
Annual Dues = $2,704
Cruise Admin Fee = $95
Savings in year 1 = $401
It's going to take a lot of $401's to pay back the $64,000 you paid up front.
Example 2
Let's say you bought 400 Saratoga points resale @100 per point.
400 x 100 = $40,000
400 x 6.76 = $2,704 annual dues every year (then adjust for inflation)
If you use a cruise swap program with one of the rental brokers, they generally give you about $15 worth of credit and don't charge the $95 fee.
400 x 15 = 6,000
Annual Dues = 2,704
Cruise Admin Fee = 0
Savings in year 1 = $3,296
Ignoring things like inflation and time value of money, your pay back period is about 12 years using this method.
There are some risks you need to be aware of and be prepared to live with. The biggest risk is that demand for DVC goes down. The cruise swap programs only work because what's really happening is your renting your points to another family. If demand goes down, it may be more difficult to rent, and you may no longer get $15 per point.
Another issue could be if the brokers shut down. You may be forced to do these transactions on your own.
I believe your fine tax wise if doing one of the cruise swap programs, but if your flat out renting your points and then using the cash to book the cruise yourself, you will likely need to pay tax on the income. That could extend your pay back period.
Edit: I probably should have mentioned, that even in the second option, your really only saving $3,300 per year on a 12K cruise. To be able to cover a 12K cruise every other year, you would need close to 800 points. 800 SSR points (most economical) would cost about 80K upfront.