Tony Gonzalez would've made some amount of sense if we either (1) thought that bringing him aboard would guarantee that we'd make the playoffs in 2009 or (2) thought we were one player away from a championship. We didn't think either of those things, so it didn't make sense.
Tony would not have made the Dolphins a lock to make the playoffs. The AFC is better than the NFC, and it probably won't help that Brady is back next year and that we play, say, the Titans, Colts, and Steelers on top of 2 games against the Patriots. I'm not going to get into that whole "tough schedule" conversation, but these games will be difficult, regardless of whether we have Tony or not.
Realistically we're not for certain one of the best teams in the AFC as of the end of the 2008 season. We hope we can be described that way at the end of the 2009 season. That means that we should focus more on hitting home runs with our draft picks than acquiring expensive talent that still doesn't guarantee anything, like Gonzalez, Boldin, or Braylon Edwards.
The Falcons made the move because they saw Arizona make the Super Bowl last year and feel like the NFC is wide open. They feel like Gonzalez makes them a playoff lock, and that Arizona has already demonstrated that any team that can make the playoffs in the NFC can make the Super Bowl.
If the Dolphins are transferred to the NFC before the start of the 2009 season, then we can reconsider whether they should've traded for Gonzalez.