Installing new ductless mini split AC alongside existing central AC

[Steven Kay]

For a 2 story, ~1400 sqft townhome, it rises to about 85 degrees fahrenheit on the second floor, while around 77-78 on the first floor during the summer weather. There is an existing central AC that doesn't seem to get it under 80 degrees upstairs during 90-100 degree weather and ultimately is kept running that increases the electrical bill.

Does it make any sense to install mini split AC in the 3 bedrooms on the second floor over replacing with a new central AC that should be more efficient? Considering selling the property (approached as a live-in flip) potentially in the next few years and wondering if I will be able to recoup part of the cost and increase appeal in the future. 

Thank you BP community!