We went to CN February 2009, April 2010, April 2011, December 2011, April 2012. While sitting on the beach on the second day of the 2012 trip I thought "what am I doing here again? I'm bored. I've done this too many times." So I went and got a cocktail, grabbed my floaty and went into the water. Then I realized that everything was just exactly perfect. It just took me a little while to get rid of the NJ stress and just chill.
A few days later my wife told me she had the same thoughts, but they soon passed. I think it is important to remember that at some point familiarity may create thoughts of disappointment. But now that I am aware of that, I easily just push that out of my mind and soak in all of the good times. We are doing CN in April, CSS in December 2014 and likely CN April 2015 (God willing). With 3 trips in a 12 month span (yep, we're spoiled ) I fully expect to run into the familiarity problem again. But I am willing if that is a burden I must bear.
(related in a weird way) Back in the day I was a big Deadhead...went to 142 shows. I think about 36 of them were at Madison Square Garden - that was sort of like my living room at one point (they would do 9 shows in a run at MSG sometimes and I would go to all 9). I vividly recall thinking "this will all come to an end someday", so I made sure to be in the moment and soak it all in, creating clear memories for the future. I do that at CN - try to be in the moment and enjoy it all.