Gvill,
Welcome!
in my experience, preventing the heat loss / gain is much more cost effective than a green method of producing that heat difference.
Sealing up the house living areas away from the non-living areas from air intrusion should be job 1. In the attic, seal all the wall headers and wire protrusions. The old fiberglass insulation will be your proof: The fiberglass will be dirty where air has been passing through, unless there have been big air leaks, like recessed lights (which are air pumps when the light is on!) use EPDM weatherstripping on the attic hatch, and get the hatch some weight with a 2x4 frame, and fill that with foam board. The list goes on...
here is a good thread on the sister-site:
Attic insulation - Fuel Economy, Hypermiling, EcoModding News and Forum - EcoModder.com