Great points! Oversight (expensive) and Limited Resources (moving target) are great solutions to most of these concerns.

One other suggestion I'd suggest, also inspired by the real world is to employ your players. Not directly of course, but make the things that make money be things that enhance game value for other players. If they're making the game better, adding content, options and etc -- f they bring value... why not let them cash out, especially if its done through the game, giving you oversight and perhaps even additional revenue.

Use the economy as a social engineering tool for your community and world.