It's not real-time, but the turn-based
Civilization series is a great game for turtleing. I too enjoy this strategy, and since
Civilization isn't so focused on combat, you have many options for building powerful infrastructures that can protect you and expand your influence. You can get to a point where your military is tiny in comparison, but your technology and infrastructure is so advanced that you can build powerful units much faster than any other nation.
Civ III is like crack.
Civ IV is a big improvement, but I haven't played it much yet. I'm too afraid I'll get addicted again.
Alpha Centauri is another Sid Meier game that's much the same, but it's about futuristic colonization. I played that for so many hours I can't remember. Give that a try too.
Sorry if you don't like turn-based gameplay, but that's how I roll. I consider
Civilization series to be a masterpiece of
4X games. Someone please set me straight if I'm wrong. I like the depth and the time to think things through.