To further my point above, here's a quote from the Herald:
"A team source said that the Cs looked into acquiring Phoenix forward Amar’e Stoudemire, for instance. Management also looked into possible trades for Utah’s Carlos Boozer, Miami’s Michael Beasley, Philadelphia’s Andre Iguodala and Golden State’s Monta Ellis."
The Celtics recognized a need for an upgrade, but they weren't prepared to pay for it. All of these teams wanted to ditch a contract with the player, and the Cs said 'thanks, but no thanks' when that was made clear.
Was it the right choice? Time will tell. But any rhetoric about spending what they need to to compete is not valid anymore.