It's been a long time since Scott Wells wasn't in the starting lineup for the Green Bay Packers. He missed four games combined in 2007 and 2008, mostly due to back problems. And when he didn't play, It seemed like the offensive line didn't function as well as they struggled with power rushers and blocking assignments. It's hard to tell how well a center is playing, but overall the quality on the interior of the line suffers when a center is a problem. And the interior of the Packers line was outstanding last season.
Also a good sign: Mike McCarthy wants him back next season.
This is a secondary concern, but the Packers don't have anyone to replace him either. Evan Dietrich-Smith would be OK if he became the starter, but he's much better suited as a backup. They would have to draft someone who could be a legitimate replacement at either guard or center, and I'd rather not have them worry about using a high draft pick on a center when they need more players on defense.
The fact that he just made his first Pro Bowl won't make him any cheaper. He should receive a contract of around five years and $25 million which would be similar to recent contracts given to Vikings C John Sullivan, and former Packers LG Daryn Colledge.