New writers needed?

Watched QoS last night. Though I really enjoyed the film, ending was superb. I thought the first 20 minutes was a bit of a mess, as if the plot didn't know where it was going.

After four films is it time for Purvis & Wade to leave the writing to someone knew? I think Paul Haggis has brought an edge to Bond, but Wade and Purvis look to have written themselves dry.