I also think that the economy being reduced to energy makes sense to extremely state-focused economies but fails to capture the potential for 'capitalism in space.' There should be a better luxury system and a trading and economy system. Pretty much all of the resources (except for pets?) are strategic; there should be exotic spices, ores, foods, chemicals, etc that can be traded. Different governments would have different attitudes towards trade and markets but clearly some sort of system would help that part of role-playing.
As to how to fit it into the simulation...it could play into growth, migration, and happiness with or without having a "money" resource. You could then settle along trade routes or at resource sources to encourage quicker planet growth instead of a more planned forced resettlement approach, which makes sense for the more statist economies. Perhaps ethics could also tie into how powerful a sway luxuries and money have over your population's happiness to make the more statist approach a more steady and true while the more free-wheeling approach has more of an opportunity for growth/production explosion as well as implosion?!
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Also, I'd hope for luxuries in a way not like, say, Civ III where they are just like strategic resources, but rather something more like "Civ B makes really good glassware, we like/don't like it and want it!"
