Example, A+ neighborhood 5 minutes away is seeing gentrification and someone buys a property that is in a D area, but maybe in 5 years they will still be holding that property and now that area is seeing a lot of growth.

No extra unit will ever berented in it.

@Michael ReilmanI installed the Aquasource Henshaw from Lowes in all 20 units I recently rehabbed and they've been great so far, and as an added bonus they're ADA height which is awesome for bad knees!

Have you added anymore units yet?  

They are using rules to add multiple ADUs.Here is a list of why adding a single ADU in dingle family  zoned areas in my CA market is typically a poor RE investment:1) The value added by the ADU addition is often significantly less than the cost of adding the ADU.

The inspections have become so nitpicky over purely cosmetic items there has to be an extra $1-2k per year to keep up with the punch list every 1-2 years.

I allow pets and charge a pet rent of $35 a month, its nice bit of extra money and pet owners tend to stay longer as tenants.

I'm interested in adding more AFH properties to my portfolio.

Since the properties are in New York you have a few extra steps you need to do to keep all of your funds out of NYs hands at closing.Here's an interesting BP thread on the South Carolina property tax issue you mentioned. https://www.biggerpockets.com/forums/725/topics/604427-south.... 

Just added this to my lease - thanks guys!