It seems possible to scupper yourself by using your last tokens/discs to build a city. Without any tokens you cannot make babies (to make more tokens) or perform an action other than "Have an idea". Unless I missed something, this is game breaking.
Well, since such situation couldn't happen for a player by an action of someone else, the only way it could happen was if the player is willing to cause it. I don't think something qualifies as "game breaking" when it is about a player doing something that very obviously would remove him from the game.
Having said all that, yes, the "last three hexes" rule (which is what prevents actual game breaking) may be annoying for some. I just don't know how much, as I've never seen someone using the "turtling strategy" throughout the game successfully...