That singular piece of joy

Instead of going down that doomed copycat road, start asking yourself questions about the outer space theme and the strategy mechanic. What's fun about each of them? Which moments in a game like Master of Orion really turn your crank? Do you like mining a planet for resources and buying new stuff? Do you like the thrill of discovering a new planet? Or does building an armada of spaceships and conquering enemies really get you excited?

Distill your game down to that one thing—that singular piece of joy. Create that one joyful experience for your player, and nail it. That's your game. Everything else is just feature creep.