Danny knows what he's doing. His first priority isn't to get us players we need, it's to make sure that he doesn't tank the team's future in trying to get the players we need.
He could overpay, and we'd have a decent team that could contend for the next two years, but then have bunch of people who'll tie up the rebuilding process post-lockout. He could also, be patient, not get ripped off in the wake of people scrambling in the aftermath of the Lebron and Wade signings, and pull something out like he has done in the past that makes us better now without mortgaging our future.
While this may be true of certain GMs *cough*Kahn*cough*, Danny Ainge is actually better informed than the fans are when it comes to the Celtics and the NBA. I think his patience will pay off this year, and if it doesn't, then his stubbornness will pay off in the next two.