There's a great implementation of this in Distant Worlds. I agree, not only does it add a nice challenge, but it also gives you more of a feel of entering a dangerous neighborhood where already there are bigger fish than you. Plus, most 4X games are all about snowballing, and if all things start equal, well, it basically feels like playing some sort of race. But if you already start behind, you can go into it with a mindset of knowing that your goal isn't necessarily just rushing as quickly as everyone; at the very least, first you need to survive and catch up before thinking about sprinting ahead... ^^
