even just the attic insulation would help out a ton - and new windows if you don't already have them.
heat gradients aren't all that different horizontally, but vertically (due to convection) are where it is at.
I don't know how the weather is where you are, but in Rochester, it made a huge difference adding some serious attic insulation.
and it is pretty cheap relative to what you save in heating/cooling costs.
(all kinds of it utterly suck to work with though - the pink panther shit smells so nasty - like rotting tuna... or as my coworkers said... well, you know)