The appraiser visited earlier in the week and found water in the basement and cracks in the cement block wall foundation.

Is the basic construction block or frame? 

You can't block air flow or the cool air will not reach everything.

In fact, googling around a little, I find this: "In a number of past cases where a mentally ill tenant violated their lease, evictions were blocked by the court until the tenant could gain access to support services or medical care to help him or her to comply with the lease in the future."

And it was hard to get to because the neighboring property put up a fence blocking access to the dirt road that people used to use to get to the property. 

This only works with a decent amount of scale. if you can pick up entire blocks you may be onto something but one random new build here or there in the hood is not a good use of your time and money.

The market here is very hyper-local, so specific streets - and even blocks - matter.

We did not build Duplexes and Quads and Apartments until later and now we have an incredible explosion of building Town Homes, blocks of Apartments and Office Buildings in Tampa.

In many places, there's a meaningful difference in property values block to block and even street to street. 

I know many of you are in California and know how (block my eyes from the gouging) high the costs are with construction in NorCal.