I suspect the appreciation will be flat if not decrease.

Sure, income will go down, but I have enough cash-flow to handle a sharp decrease in revenue.

My monthly rents would probably be comparable to what the new apartments are asking for and decreasing the rent breaks the 1% rule.

Or would a roll roof be a large decrease in value?

Most sellers are not going to fall out of escrow for a slight decrease in their net.  

Yes, those things absolutely will affect the value of any home you purchase.The better question to ask is what is this house worth today, and is it likely to increase, decrease, or stay the same in value? 

Until there are other locations outside of CA that are similar or if immigration becomes tighter, we might not see a decrease in population at all.Thoughts?

In that case you can also take bonus depreciation and accelerate 100% of those costs into the first year, further decreasing your tax liability.

I don't know how bad it'll be but we can assume that properties in these areas will see a decrease in value.

Increasing your portfolio size will INCREASE your margins...not decrease them.Using the BRRRR method will actually slow you down...not speed you up,...and WILL decrease your margins.