As a fan, it's sad to see dedicated, hard-working players like Trot Nixon are not re-signed. He gave the team everything he had and it's probably why he injured himself so often. I'm sure he would have re-signed with a hometown discount.
I'm sure the Red Sox were looking at Nixon's stats and the declining number of games and power. His slugging average has dropped from the .500s to the .400s though he's maintaining his OBP (maybe the A's will want him). Meanwhile JD Drew has stayed in the .500s even coming off of an injury year.
There's one thing that most don't factor in is that Nixon does poorly against left handed pitchers (LHP). Typically, Nixon is not played on days with a lefty starter. This reduces managerial flexibility and pumps up his statistics. Drew vs. Nixon against LHPs is .814 vs .620 OPS and .263 vs. .207 BA over the last years. That's a huge difference.
The one thing is character and Nixon has it in spades. It is telling that someone is willing to opt out of a $11 mil/year contract for a $14 mil/year one. We hope the atmosphere of the team is contagious.
If you want a real in-depth analysis, go to the Dec 6 post of the Weekend Sports Page. It's really well put together.