Are there things that can cost-effectively be done in existing houses? That seems a good way to create demand for greater efficiency - demonstrate the value on a smaller scale first.
Yes. Low-flow shower-heads can pay for themselves in a few weeks. DIY air-sealing with caulk and sprayfoam will also pay for itself in a few weeks in most old homes.
LED lights pay for themselves in a few months if you get a good price on-line or from a home center.
Added attic insulation is another thing that will pay for itself in a few months DIY, or a few years if you pay to have it done.
The high impact retrofits are better windows, more insulation and new mechanical systems.
Getting insulation into walls is hard and at some point doesn't help a lot if there are air gaps.
New mechanical systems aren't really cost effective (because operating costs aren't that high; hundreds of dollars of monthly savings on a $10,000 upgrade). For people that use a lot of cooling replacing an old air conditioner can be a big win.
LED lights pay for themselves in a few months if you get a good price on-line or from a home center.
Added attic insulation is another thing that will pay for itself in a few months DIY, or a few years if you pay to have it done.
BuildItSolar has a slightly dated but still useful section about cutting your energy use in half at: http://builditsolar.com/References/Half/Half.htm