Here is what I believe. If I have to calculate how many trips to break even on my DVC purchase, then I should not have bought the DVC to begin with. I know that I am a cheapskate and I know that I am staying in a much much nicer hotel than I would be if paying cash. I am very happy with that. I know that I paid significantly less buying resale than all the people that are buying direct right now. I know that I get to go to Disney 4 or 5 times a year. I know that if I did not own a bunch of DVC points that I would go maybe once and probably stay offsite some times.
Now if you really want the formula you should use: (Cost of points+closing costs+ any finance fees+(yearly maint fees+(yearly maint fees*1.3% per year that you are going to own)-the cost of whatever hotel you were going to stay in (be real here use the all stars not the GF grand villa cash price)* the number of trips per year you were going to go (this number might be .5 or .25) now add back in the number of trips you will be taking because you have a few more points that you need to use up plus the cost of airfare/driving plus the cost of food (not the cheap places you are in the DVC now so we are talking table service and you can deduct the DVC discount from that), plus the annual passes that you are inevitably going to buy, and don't forget the extensions or extra trips because the are having a DVC party in one of the parks, plus the extra points that you will also need eventually, plus the DVC special merchandise you will be buying, plus tipping bell services when you have a split stay because you cannot get a full week the 1st week in December in a standard at BLT and need to go to BWV for 1 nite and then AKL for a nite and heaven forbid SSR for the rest of your trip (of course all on your SSR points) plus the cost of your time stalking the DVC website looking for those extra days every 15 minutes plus the extra luggage you will have to buy because you are going so much that the airlines tear up your current bags, plus the cost of dog, cat, ferret, etc boarding, plus extra sunscreen umbrellas, ponchos, snacks less the cost of renting your points (but seriously you don't have any extra points to rent you need more points)....Well I think you are beginning to see why the calculations are pretty useless.
Take solace in knowing that you are going to have some really really nice vacations.
Now I have to go see if I have enough points to squeeze in another trip some time this year.