A lot of people up north have them but also have a back up supply for heat due to them not working well or efficiently when the temperatures get very cold. 

Climate change is coming for Florida in a big way and between beach erosion, sea level rise, and rising temperatures, I think more people will be looking to vacation north of Florida in the future.

No because people want different temperatures and have different climate control habits. 

The owners of the other adjacent home have been on an extended vacation (and have left their air conditioning set to 85 Fahrenheit).A few weeks ago, my tenants called me saying that their AC can't maintain setpoint--I assured them that this is normal as both demising walls are currently exposed to elevated temperatures.

Wouldn't hurt to get a smart thermostat also to help regulate temperature when you're not home. 

When I get some rentals on the same property then I will hire a towel/linen service which washes everything at the lodging standard temperature.

However, it’s hot here and so is the temperature, haha. 

Lowering their temperature certainly leads to longer term tenancies. 

Cracks depend on a hundred different factors such as humidity on the day of the pour, ambient temperature currently, ambient temperature on pour day, etc. 

Behr marque can be used at lower temperatures.