It's also worth considering that the current prices are a reflection of extremely limited supply. There's no point in setting the price to 1 million gil or less if you're going to have so few plots. If you're going to have people fighting over limited availability, and given that this also serves as a gil sink, might as well siphon off as much gil as possible for now. But that's also why the land is on a fast depreciation schedule (half price in a month), and supply will increase. Once supply increases to keep pace with demand, then the prices will drop.

Really, the main issue is that, no matter how busy the server, and thus how high the demand, they all have the same amount of supply. If they could solve the issue of supply (have the right amount of wards/plots for each server), then it would also resolve this issue of price over time. (If you knew that there would still be plots available in a month when it goes from 4 million to 2 million, you could just wait for it.)