Note that the issue with energy is actually extracting it, and that the easier it gets, the more I guess "futuristic" our economy becomes. We pay way less energy to get food and high-tech gadgets now than we did 100 years ago. Once we have enormous amounts of plentiful energy compared to what we have now, we'll no doubt have some technologies and quality of life we can't even dream of right now, but we will still have energy scarcity to "pay" for those incredible things we'll have. (e.g. you're currently not paying for energy to transport stuff between planets, because it's stupid-expensive. In the future, despite millions of watts of energy being possibly cheap, you would still need to spend billions of it to transport stuff across space).