[Greenbuilding] Improve or Build New

[sho11 at comcast.net]

I know there was some discussion about this topic a while back but I am curious what you all think of my situation.

My present house seems to have been designed to be as bad as posssible in every way connected with energy efficiency.  It is shaded by trees and hills in winter and gets full sun in summer.  It has windows equalling 15% of the floor area facing west! There are a total of 33 windows! The  walls have poorly installed R-11.  The raised wood floors have no insulation.  The open beam ceiling/roof had a layer of Thermax foam 2 inches thick.  I have since added 6 inches of Icenene and 6 inches of Fiberglass.  The windows are aluminum frame dual pane but older and somewhat leaky.  It is two story and 1900 sq ft.

Here is the dilema.  I want to buy a lot and build a really efficient house.  It would suit my needs better, be cheaper to operate etc, etc.  I would feel good about adding a well built, energy efficient house to the local housing stock. Would it be a better solution than trying to improve the present house?

What are the tradeoffs?

Thanks

Steve