I've pretty much been expecting this since the time that he was traded for on January 22nd in what will always be referred to as the "Jon Leuer Trade" within Cleveland circles. The Cavaliers traded reserve forward Jon Leuer for Speights, Wayne Ellington, Josh Selby, and a future first round pick. While the pick is clearly the most valuable part of the deal for the Cavs, Speights and Ellington did combine to stabilize what was a mostly horrific bench.
In his time with the Cavaliers, Speights continued to post excellent per-36 numbers, as his been his M.O. throughout his career, with 19.8 points and 9.8 rebounds. The reason that Speights hasn't ever been able to see more consistent minutes throughout his career is because he's normally a pretty inattentive defensive player. Still though, when matched up with someone in the post he does effectively use his body to push guys around.
I think he probably made the right decision opting out. The option on his deal was worth $4.5 million for a single season. Given that a lot of teams have cap room this offseason, along with the fact that he's still an effective bench player, I wouldn't be surprised to see him pick up a three year deal worth anywhere from $10 million to $14 million.