Well That Day Has Come

Most players will eventually "catch up" with the game. Whether you lose interest at that point will vary among players. As some of the other posters have mentioned, one possibility is to take a new approach to the game, usually based on city planning... but others have focused on themed tasks for their characters, staging great screen shots... Compared to other
App Store games, I'd say that TSTO is above-average in the potential for creative play that it affords caught-up players.

The boards here have long featured a mix of wheat and chaff, and differing opinions on which bits are which.