At some point, demand decreases or stagnates at the same time supply increases, resulting in a sharp drop in prices — and the bubble bursts."

You need to decrease the amount of your own cash invested to get a better return. 

So as you move up in rental price, the amount for repairs will become a decreasing percentage of the rent.Now as that applies to capex, certain capex items will be relatively fixed or fall within a small range like a water heater in @Ned Carey's example.  

., from what I can see, the first property is simply not that great of an investment unless you are able to either greatly decrease the purchase price or generate additional rental income/decrease monthly expenses.

(Excluding <5 unit properties,) The total value of your multifamily property increases as cap rate decreases.

-As equity liquidity increases, the negotiating power of shareholders will decrease.

As large industrial cities have fallen by the wayside and populations decrease could this be a turning point? 

Don't fall that she will give you the keys herself.We stopped excepting Sec 8 2 years ago and our R&M expenses decreased from 18% of total rent to 9%, which increased the net income by almost 30%

If I had this exact same house in an area that drew rent at $1200 a month instead of $1800 a month, can I really expect that my expenses would decrease simply because the exact same house is 20-30 miles in a different direction drawing less rent?

All it will take is something like another decrease in our credit rating or some unforeseen panic and we will not be able to sell government bonds at the rate we want.