Agreed, i really like the idea of ships having limited range especially. Jet makes good points about being able to just fly in and capture homeworlds ignoring other colonies/outposts in the process. And if you limit ship range, that would to a degree limit the land grab as well, even if PCC didn't limit the range you could colonize. You'd be able to colonize further away in the long run without limits from PCC, but you'd have to build colonies or outposts along the way to extend your ship range in order to colonize further away.
And as ChickenHawk said, capturing homeworlds is really not hard. I've captured 6 in one of my games, and control my entire starting sector (galaxy? Whatever you want to call it) outside of like 1 or 2 non-homeworld colony and an outpost or two. Beyond that I have countless colonies and outposts (I sstarted out playing as a harmless trader. Then someone attacked me (and eeryone else in my starting sector) and captured pretty much every outpost in the sector. So i turned around and captured everything he owned. After I found out that you can meet any victory condition and I realized that there's no way I'd ever be able to trade 4 billion common ore to be able to win, I figured I'd see how hard a warlord victory was. The only homeworld that's been a problem to take is the one that had stealth orbitals so I couldn't kill them. Beyond that, I've killed several outposts with a few defense orbitals, or mines, or a coupla ships, and several that have been 450-500Mu population.
Non-homeworld colonies (and non-terran so less population) are even easier to capture.