Either 1) get out of the way and let the market work, relatively free from restriction or 2) suppress market forces for so long that eventually the city decays as the original base of wealth is siphoned off by high taxes or those people choose to leave.

Well, much should be addressed in the lease, housekeeping issues, keeping the property free of waste, decay and degradation, that means, wipe the walls down!

Neighborhood decaying.

Depreciation basically says that the physical structure of your house will decay and lose value over a period of 27.5 years because everything will need to be replaced like the roof, siding, appliance, etc.

Obviously, there are still other factors, but things like over-building are less likely to counteract the socio-economic and population trends, as new construction is rarely competitive for rental units.So, the metrics you list above are much more likely to help you determine whether market demand and cash flow will remain strong as opposed to whether values will increase and what extent.The problem is, the property you've been discussing won't likely cash flow at all.

Much of the older - 1960s and 1970s - product lies in flat or slowly decaying C neighborhoods. 

The trick is to use these activities (research, reading (knowledge), and analysis) to counteract the inner negative voice telling you otherwise. 

All that fading you see is the granulation keeping the sun's heat from damaging the shingle.If you coat that granulation with black paint or tar, you're counteracting that sun reflection and the shingles will overheat and cool from daytime sun to nighttime cooling.

That means that whatever radon is there on any day, 3.8 days later, half has decayed to another substance.

Also, 3” is a huge section of decay— usually these are caught at about the size of a dime (because they leak).