added bathrooms, making a total of 3, one bedrooms is in suite, created an open plan, contemporary kitchen with a large island, finished attic and basement, added central heating and air, provided amenities people like as fireplace, wine cooler, wine cellar, smart thermostat and key lock, but mostly we created a contemporary home where there are not many What was the outcome?

The other way to do this is to have a heat treatment done.

I re-sided a substantial portion of the exterior, added heat pumps to all units, new windows and finished out the basement.What was the outcome?

I was able to put in all new plumbing, electrical and heating/ ac which are all coming online now.  

I eventually realized this when considering what it would take to break out the heating in a 4U I bought with a steam boiler or the insane cost to replace it with individual systems.

I’m sure the answer is: it depends on your situation, finances, etc...BUT...I’d be really curious to hear from a more strategic perspective if you all would go for cost-effectiveness and renovate both units with basically the same design elements, materials, colors, etc....

Paying taxes and maintaining the property are elements of the 5-year SoL under Sec. 16.025. 

Also, I expect to outperform over the long term with repairs too due to the fact there is no central heating and air currently.

A common big expense is undetected collapsed sewer connection in older buildings, roof of course, AC & Heat, increase in property taxes, and on and on.If the presidency changes hands, taxes and regulation are promised to escalate & I don't think your cash flow is sufficient to deal with it.

Maybe some element of timing, such as having x# of days/months to change categories, terminology?