Ask anyone who works with numbers for a living about how to estimate true costs. I have absolutely no doubt that they will say it needs to include MF plus depreciation plus opportunity costs. Are the depreciation/opportunity costs "uncertain"? Of course they are. However ignoring them is like closing one's eyes; feeling the tail of a donkey and concluding that one has caught a snake.
DeniseM was right when she said that it is cheaper to simply buy SPs from Starwood rather than purchase a TS for the purpose of converting. Your math suggesting otherwise is fuzzy because it ignores important facts pertinent to the situation.
As LisaRex points out the limitation to purchasing SPs is that this is restricted to 20K per person which does not go very far either for hotel stays or airline tickets.
I usually stay out of these "cost" discussions because they are not as straightforward as some portray.
Nonetheless, a few additional variables to consider when evaluating the ultimate cost and value of a timeshare:
Residual Value. Some assume zero, some less than zero. Others make an assumption based on current "market" value.
Roshiguy and DanCali call the cost "depreciation".
At some point in the future the actual cost must be reckoned with. How it is reconciled remains unknown, and is based on the circumstances at the time.
For example, owners A, B, and C buy timeshares at a cost of $75,000. Each use them for 5 years, then sell.
Owner A sells for $25,000. Has no offsets and experiences a real 10k/year devaluation.
Owner B sells for $25,000. Needs a 50k loss to offset gains elsewhere, in the year sold.
Owner C waits outside the sale center until he sees a couple walking out with a new owners package. Approaches the new owner and offers to sell them the same timeshare for $50,000. The new owner accepts the offer, and recinds the purchase.
Although price and ownership term was different, each of the above examples are actual events we observed in the past 90 days.
Bottom line is that one should not assume unrealized capital cost until it is sold.
Opportunity Cost. This is perhaps the most misused term in timeshare cost "analysis". It is theoretical, and almost always has no basis in reality. It presumes that in the absence of the discretionary timeshare purchase, there would not be an alternative cost of accommodations and travel.
If this is the case, there would
no financial justification
for the timeshare purchase in the first place.
Almost always, the alternative costs will exceed any return on retained capital.
Which brings me to
Subjective Value.
This is a highly individual perception of value (not cost).
Interestingly (to me anyway) those that can truly claim a real opportunity cost vs a timeshare purchase, are those most likely to place a high subjective value to issues like "VIP Status", and other preferential conveniences. It is hard to quantify in purely dollar terms.
The more cost conscious among us watch our dollars more closely.
I am reminded of a very talented, energetic, highly successful surgeon I am acquainted with. Vacation cost is not an issue he concerns himself with. He pays for the pampering which he believes he needs to escape the pressures of his profession.
Others handle the mundane details of arranging it.
His reality is different than mine, or most I know. But, it is his reality.
While this is a more extreme example of subjective value, it tends to make the point. There is a subjective value to Elite Status that cannot always be debated on purely financial terms. The value is in the eyes of the beholder.
I am not debating the validity of the analytical approach taken by some. It is their reality, and it how they choose to view the matter.
I do, however, take exception to the notion that theirs is the only "right" cost analysis.