Interesting. There's a lot that goes for a campaign that runs for so long, particularly with the same players. The obvious advantages that with each passing year of play time, the players become more intimately familiar with the campaign, it's social customs, and culture. Players can get really into character after such a longevity and jump right in with a character. The experience of immersion gets deeper with each restart of the campaign.
Also the campaign breathes or becomes more believable if the GM continues to make the world grow with the players. I ran two campaigns set in the Kingdoms of Kalamar--the first campaign was the Age of Worms AP from Paizo, but I used a lot of the backstory, politics, and impending invasion. The second campaign started just 12 years later with the old PC's having progressed well into their roles as leaders, teachers, and nobility while the second set of players has to deal with their own problems and impending doom. Also a lot of the events that the first group left unfinished became the serious buisness for the next group.
For the four or five years that my players have been playing in this campaign, it makes for a really easy understanding of major NPC's, customs, and political maneuvering.
Congrats on your long term campaign.
