Well....that's a lot going on there.

#1 question is..Is the existing heating and cooling equipment the correct size to heat and cool the whole house?

Are the other 2 bedrooms uncomfortable too?

How possible is a future attic renovation?

My personal opinion is that your biggest "bang for the buck" will be to insulate your attic and attic stairway door first.
Then focus on shading any windows that face east or west, as these will have the largest solar gain. Both upstairs and downstairs.

And if you haven't already, switch out all your incandescent light bulbs to CFLs. This lowers your heat that is created inside the home that must be conditioned.

Once that is accomplished, then look at the heating and cooling load and ductwork, and figure out the best thing to do.

Make sure to look at your home's electrical capacity if you are considering adding a second system.

My gut reaction would be to enlarge the upstairs vent sizing to be larger, and to get the return air as good as you can. Have the bedroom doors been undercut (that is do they have about 1 inch or so cut off the bottom) ? This can help with return air.

Best of luck

Adding ductwork can be a major construction project. That's OK as long as you know that going into your decision. A mini-split heat pump/ac unit (ductless) may be a good choice if major ductwork is an issue. You can even put in good ole window units to cool the space down if aesthetics aren't the major concern.

You should still concentrate on additional attic insulation and tightening up the envelope to minimize air leakage, whichever direction you decide to go with the cooling system. That cuts the heating and cooling load and pays you back every time you get your monthly bill.

kitty

1.insulation

2.new DP windows

3.additional return(s)on 2nd floor

4.damper on supply line to get air to second floor-perhaps a booster fan

IMO

Thanks for all the advice! Here are the answers to your questions,

1. I believe the unit is pretty well sized for the house. One HVAC tech did the math on airflow and said it was a bit air starved (metal contraction sound when it kicks on.

2. The smallest bedroom is too hot in winter and too cold in summer. It's a very small room. The 2nd bedroom is a guest room no one sleeps in and generally seems ok in temperature and truly in the middle. The master bedroom is of course the nightmare.

3. We wouldn't renovate the attic any sooner than 5 years.

4. The bedroom doors are undercut.

There is a bump out that runs the supply to the middle bedroom. The bump out is 18"x18" but the supply duct is only about 6 inches in diameter (so says one HVAC tech). His suggestion was to run a return up that bump out, build another bump out in the 2nd bedroom to run the return into the attic and have the return in the 2nd floor hallway. That was the $5K solution.

In the basement the furnace is directly below the master bedroom. No one who's been to the house has mentioned running a bigger return or an additional supply to the master, but maybe that's because they assume I wouldn't want to tear out part of the wall in the living room? That seems logical to me but maybe I'm missing something?

Thanks again everyone!

There are ways to ventilate attics with no eaves. There was a post in a Gardenweb not that long ago. I have seen pics of the equipment, but I have never seen it in real life. You flash vents into the shingles. It probably works best with highly-sloped roofs.

Who is doing the energy rating? I hope that no one that is selling your something, but independent. "Fire" anyone that says to install a powered attic ventilator. Generally, they keep the attic cool by sucking the conditioned air out of the house. You need to seal the attic from the rest of the house and the attic door is probably just the start. Do you have recessed lights in the ceiling? How many holes have been drilled from the attic to the living space to add power circuits, telephone, cable, computer,...?

In my neck of the woods, hot and humid, the typical modern advice is to seal the attic and insulate the roof deck. I don't know if that is appropriate in the mid-Atlantic. A good energy rater should know. Given your attic ventilation challenge, that might be easier. It eliminates the need to seal the ceiling and nets you some nice semi-conditioned storage space too.

Sealing the attic puts attic ducts inside the house envelope, which is where they should be. Ducts will leak. If supplies are located outside the envelope, they shoot conditioned air out of the house and depressurize the house sucking in outside air elsewhere. Returns do the opposite.

If additional ducting is too difficult, heat pump minisplits might be a great solution. Keep in mind that you can install two or three indoor units hooked to one outdoor unit. The bonus is that you can get some inherent zoning with this. In hot weather you can leave them off if you are not in a room. When you are sleeping, you can leave the main system off. With heat pumps, you can keep the area warm in cold weather leaving the main system off. The trouble I found with minisplits and especially multisplits is that not all contractors like to work with them.