I don't know about projecting
accurately but I've done some work on tracking historic MF changes.
Feel free to take a look at my Google Sheet -- and make your own copy if you want! I'll summarize some of the data and include some charts here, but they'll be blurry, so you can click-through for higher-resolution versions, and make your own copy to play around with variables.
https://docs.google.com/spreadsheets/d/12UuW8kj1JsUG-M16dHppNFc_in0Mic-b5qpszwZ17vY/edit?usp=sharing
The 'Detail' page tracks annual changes for each resort and calculates the historic Compound Annual Growth Rate (CAGR). For resorts that have been open long enough, it also splits out the CAGR for the first five years, last five years, and middle years (excluding first five and last five). At
most resorts the growth rate is slow for the first 4-5 years before there are material increases, so that's there as a reminder not to look at a limited dataset and assume that, for example, RIV will always have due increases half the WDW average.
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There are also some visualizations of changes per resort.
This chart shows the % change by year, so you can see how much dues at each resort have grown since opening. This visualizes how BLT dues growth has been significantly above-average, doubling in its first 15 years. BWV has been consistently below-average, taking 25 years to double its opening dues. SSR saw relatively little dues growth through the first 15 years, but is now somewhat above-average relative to opening-year dues.
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This chart shows the dues in dollars, from each resort's opening to the current year, along with an average (black line).
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This chart projects dues (in dollars, log scale) out to the end of each resort. This uses the "Proj. CAGR" value for each resort in the Detail slide (row 45), which is something I just filled in as a guess based on historic data, usually in the 4.0% to 4.5% range. Obviously there's no chance these will end up being perfect straight lines, but it gives a rough idea of what you're in for.
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