Suppose rents increase at 2%/Yr over the next 30 years, inflation averages 4%/Yr, and your current total rental income is $10,000/Mo, here’s what happens to that income in today’s dollars:In 10: years $8,235 (a 17.65% decrease in buying power)In 20. years: $6,782 (a 32.18% decrease)In 30 years: $5,585 (a 44.15% decrease)So even though your rent increases to $12,190 ($10,000 x (1 + 2%)^10) after 10 years, inflation erodes its value to the equivalent of $8,235 today.

However, this will decrease your tax basis in the property and any amount you deduct as depreciation will be taxable at the 25% capital gains rate for real estate when you sell the property (assuming you do not take a loss on the sale).As has been mentioned already, taxes are a tricky topic and the laws change all the time.

Focusing on paying down the principal, means you are building equity in the property and every bit of equity you gain, that equity decreases the total return the equity is providing you. 

It looks like it stopped decreasing in population and even started to increase a little.

Airbnb does punish those going against their grain with decreased visibility.3.

Decreasing?

You can find higher ROI (on paper) here and probably in other cities…but the probability of actually collecting rent significantly decreases.

I can't decrease it, but I can avoid adding to it. 

The appreciation historically been too high to suggest an unleveraged purchase as the return decreases.  

It decrease property values if you're nearby.