I've long held the theory that former players as color guys have a window in which they have peak effectiveness, and it's generally year 2 or 3 through year 6 or 7 of their time in the booth (especially if they are immediately thrust into a A or B team like Romo was). A year or so to settle in and figure things out, then they shine for a while. Somewhere around 7-8 years removed from active play, they start to lose touch with being a player and the day to day grind (marked by the fact that at least 80% of the guys they played with are out of the league). By year 10, they're believing their own hype and getting full of themselves and generally become more annoying than insightful.
This applies in any sport's national broadcasts...true of Simms and Collinsworth as much as it is about Joe Morgan and Tim McCarver.