"We're stuck with fossil and fission for the forseeable future. And in spite of their problems, they will give us at least a few decades, and at most, a century or so to transition into a new energy economy."

That's about how I see it, and that is why I think we are taking too long before getting into the space environment. In space environment energy production can be massive and far cheaper than on Earth- supporting human populations in the trillions and for thousands of years. And there could be technological leaps related to this, that makes this a severe underestimation.

"The one thing we can do right now is figure out ways to conserve. We need to reduce energy usage, develop more efficient ways of using the energy we can't do without, and to modify our society and infrastructure in such a way that we do this without breaking our back economically or drastically degrading our standing of living (that would be politically impossible)."

If you are looking at global energy picture, probably your greatest potential in terms of conserving energy will be in relation to countries like India and China [and Russia]. Another area could be related to electrical grids- or moving electrical power efficently.
Also probably something needs to be done about the refrigider appliance, since it sucks so much energy. I would need to know more, but suspect that people could build walk-ins as part of house, they would not only get a better fridge, but could cost less to run. Everybody uses these things [they are essential] and little attention is really paid to this.
Another area is in public lighting, you should able to use LEDs instead conventional street lamps- this would save a fair amount energy and get us darker skies- another huge value in terms of aesthetics the city planners are mostly neglecting.

As far as transportation, I think the current Information Age, is going to radically change this- business is already transforming itself in this regard, governments are and probably will remain lagging in this regard.