I wonder if there will ever be a cap. Eventually the dues will just be too much to justify people buying DVC or keeping it to more and more people
Aside from what I believe is a cap on what can be raised in a single year, there is no cap, and there never will be.
Dues reflect the costs of the resort you own at, period. There is no profit or wiggle room or anything else that goes into them.
In essence they add of the costs of all operations (bus service, front desk, housekeeping, activities, power, water, reservation CMs, landscaping, security, legal fees, filing, property taxes, etc) and they set aside an amount for capital items (parking lot resurfacing, roof repairs, painting, refurbs, etc) and then 12% for "management costs". They add that all up, divide by the number of points, and that is the dues per point. And yes, DVC pays dues on any points it holds.
The only way to lower, or keep dues in check, is to lower or keep in check these costs. Now you can make an argument that this is a case of the fox guarding the henhouse - in other words the WDW Transportation Division is overbilling DVC for the bus service it provides. However all of these costs are independently audited.
Points go up as cost of business goes up with inflation. You can argue that things are being mismanaged, and that is a valid argument, but as far as how dues are calculated, it is based on cost to run the resort.
You can also argue that the 12% of costs for management should be lower, but it is what it is, and it was in the contract when you bought DVC, provided people read it.