I'd add that we not only want, but need, space travel in order to maintain the species. Once our sun or planet dies we go with it, unless we're on a different one.

Not just that even more mundane stuff becomes much easier if you have more energy - clean water (desalination), trash (vaporize & collect fractions), raw materials (can trade energy for lower input concentration in ore), polution & greenhouse gases (capture back from th atmosphere and convert to something usable or inert).

All this becomes relatively easy if you have a lot of cheap power. And you would not get it just by power saving and eficiency improvements, only with research and building of new sources.

No, we need to use more of what we get. We don't use hardly any of what hits the earth. I believe I read that the Sun supplies 50X the amount of energy we consume (if of course we could capture it as energy).