All but a handful of our properties use electric resistance for heat with no AC.
We have, however, replaced a number of heat pumps, a mini split and a gas furnace.
The gas furnace was about 50% efficient and took about $500 in maintenance. At the time it was owner occupied. I figured a three year payback for the upgrade. We later rented the house out and the lack of service calls alone was worth it.
While the house was rented the AC went out. It was a split unit at about 10 SEER. We had it refilled with R22. I suggested replacing it but it was twice as much to replace as recharge.
A year later it went out again. We replaced it with a 26 SEER mini split that the tenant loved.
We kept the tenant for two years and would have kept her for longer if we didn't decide to sell the house. Affordable energy bills was part of that equation.
On our office building we've been replacing the 10 SEER heat pumps with 14 SEER units as they fail.
My observations? The cost of R22 is prohibitive. Don't ever buy it. Instead, replace the unit.
Efficiency matters as your tenants have a monthly nut and failing to pay either you or the utility bill is a showstopper for you.
New equipment will be more efficient than old equipment. It's illegal to sell 50 AFUE furnaces and 10 SEER AC units, but millions of them still exist.