Actually, there's a trick I recently discovered that would have completed this game the 3 turns sooner: Complete 2 Great People at the same time. i.e. if two GP reach 300/300 on exactly the same turn, you get them both. I don't know if the game increments the counter twice, though. I also don't know for sure if this applies for two cities, i.e. if different cities complete a GP on the same turn. I know if the same city completes 2 GP, it does it. That'll save you a cool 100 GPP. The Hanging Gardens is important for your trade routes. The value of every single trade route is calculated in large part by the population of your capital. Though I suppose if you're going for cultural win, you might not have all that many trade routes. Also, as CYZ said, it enables you to have more GA specialists.