Yes.
TD needs to play the five and the Spurs need to get a versatile four man that can play low or on the perimeter. He also needs to be able to play the three when the Spurs need to go big.
I think finding that player will determine if the Spurs will win another championship. The respect Dirk Nowitzki is receiving this year is sickening. If, and it's a big if, he wins a championship, you won't even be able to breathe on him without being called for a foul. The Spurs need a player that can matchup with Dirk well enough to make him work on defense and make him feel uncomfortable on offense. Lamar Odom comes to mind. Someone that has similar size and a similar game to Odom would work. Of course, combing Europe for another Andre Krilenko would fit the bill, talent wise and financially.
The long three is a quick fix. You need a player that can play the four and the three to completely solve the problem, imo.