HVAC replacement, options for upstairs
A routine HVAC checkup indicated that our AC compressor and fan are at their end of life based on Megger tests, so now I am thinking about our alternatives in replacing the AC system. I expect to be talking to a number of contractors to see what they propose, and I would like to get ideas for what can be done in addition to replacing the air conditioning.
One issue in particular that I would like to address is that the upstairs of my two-story home tends to be significantly warmer in the summer and cooler in the winter than the downstairs. In summer, we then have to mentally account for the temperature difference when we set the thermostat (downstairs) for nighttime so it will cool off the upstairs enough for us to sleep comfortably. I think that one of the more significant things we can do to make our house more comfortable to live in is to get better regulation of the temperature upstairs.
I don't know a whole lot about heating and air conditioning, but my ideas would be to consider improving the attic insulation somehow and/or to somehow have the upstairs and downstairs temperatures able to be regulated separately. The technician who was out to check the air conditioner mentioned a variable-speed blower as a possible help, but its not obvious to me how that would help.
Also, at some point in the future, we would like to finish the unfinished basement. Does that make any difference to selecting an air conditioning unit now?
Any ideas or advice? My feeling is that contractors will be focused on selling and installing a new central system, not looking at other aspects of the system or the house as a whole.
Possibly useful background information
Location: Omaha, Nebraska
House: Two story, approx. 2100 sq. ft not counting 1000 sq. ft. unfinished basement
Age: Constructed ~1996, still has original HVAC system
Heating: Natural gas furnace
Attic ridge vent was added to roof last year and has seemed to help the summer temps upstairs somewhat
Attic insulation is 12 - 14 inches of blown in fiberglass
HVAC vents are in the floor downstairs and through the ceiling upstairs with return registers near the floor on both levels