The assessed value of a property is only indirectly related to the property tax that the owner pays. Municipalities multiply the assessed value of a property by the mill rate to calculate the taxes. They set the mill rate essentially by dividing their budgetary revenue needs by the total assessed value of all properties in the municipality. If my assessment goes way up (say, I put an addition on my house), then my taxes go up. But if everybody’s assessment goes up proportionally, then my taxes don’t change, because the mill rate will drop.

The latter is the situation in those ski-resort towns. It means that property owners suddenly have a much-higher net worth, but doesn’t necessarily mean they’re paying more in taxes. It only means that if the rich people moving in demand more and better municipal services, and raise spending.

On the other hand, look at the perverse incentive built into the current system: Landlords can reduce their taxes by letting their properties decay (lowering their assessed value); or at least, the system disincentivizes improvements which raise the assessed value. In a popular ski-resort town, or college town like mine, we get slumlords, because the vacancy rate is so low that they know that they can get tenants even in run-down units.