
I recall seeing this "effect" in motion in the game Sins of a Solar Empire. It looked very pretty and gave the idea of having millions of people down there going on about their business. If played right, this effect could serve the gameplay and provide a visible cue on how much of a colony is on a planet's surface. It would also help to estabilish/reinforce a sense of scale in the player's mind.
Been a while since my last visit, and maybe this was suggested already. Don't get mad.