The Noobstown spawn actually changes occasionally. Like for the Christmas holidays it was all snowy and there was a huge tree with presents underneath. For Hallowe'en there were pumpkins and scary things. And when there were new features, such as emerald trading, or pistons, these were also reflected in the spawn area. If you are talking about changing the whole spawn, ...then that would be a rather massive undertaking. But a valid suggestion indeed!
The spawns in each town can be made new, you just have to speak with the mayor of the town, or perhaps their head architect. Over time, I've seen towns redecorate their spawns, and even moved it to more convenient places. Town staffers consider changing their spawn in order to attract more residents to their town (just as you have implied: new spawn=more people).
...restarting the world? Now that's ...for a different topic.