re: Home Insulation/New Windows - Advice needed

Curious what size (tonnage) is your HVAC? What is your relative humidity like in the house - is the HVAC able to keep it near 50% RH or less during the heat of the summer with long AC runtimes?

Often the issue is HVAC is not the equipment itself but the ductwork - to small, leakage, not enough return air,... Did the HVAC companies provide a thorough examination of the ducts, sizing, leakage, etc., or did are just checked the equipment function?

Perhaps you should pay to have an energy audit done with blower door test and that would provide with information how leaky your how is with regards to air infiltration and where to direct you efforts and $$$. Companies can also conduct HVAC duct leakage tests - often the same company that does energy audits.

If you have condensation on the inside of double pane windows they have been breached but there are companies that specialize in repairing that issue cheaper than replacing the windows.

I will say at the temperatures you keep your house at, 70 and below, you are taxing the operational limits of a any properly sized HVAC system, during heat of summer. If humidity is maintained near 50% or less in the house, most people will feel more comfortable at higher temperatures.

Not saying you don’t need new windows and better insulation in your home, but before dropping that kind of $$$ on those projects I’d pay someone to do an energy audit/blower door test that will tell where to best direct your home improvement efforts.