42,
I know the link I left a few post back may not have stood out so here it is again.
Free Home Air Conditioning! - Save Money on Air Conditioning Bills
I realize it is a long read and the person sounds a little pompous but what he describes seems well thought out. If given the yard space and initiative I would think one could keep their outdoor unit close to it's SWEET range year round using this closed loop setup with the outdoor compressor driving it in a kind of push pull configuration.
You mention adding on another large heat pump for basement or main floor or both, are you familiar with multi splits. One of the most reputable brands sells here now and while I'm sure would cost more than your 12k unit x however many rooms, it still may offer many benefits for your additions as opposed to multi smaller units. Especially after you put in the cheaper electric supply meter you spoke of. Expensive I know but 3-4 ton from one outdoor unit and up to 8 indoor units of varying capacities.
http://www.daikinac.com/residential/...-%20Daikin.pdf
Just zone the whole system so it can condition the area your in at any time of day. Just look over the specs and see what you think. Now think about the one outdoor unit driving a closed loop earth tube system and what do you think you could save now.
Just a thought Paul