The agent connection is vital these days. A good agent is someone who will assist you in handling the commercial aspects of your career, serving as a conduit for a multitude of issues that will arise throughout the publishing process.
What the agent is not, however, is equally vital. An agent is not a miracle worker. These are tough times in the publishing arena, and the agent can help accelerate the process, but not create a contract out of thin air. The agent will help you bridge the divide between what you are comfortable working on and what the publishers may want - and more than likely this will mean further rewrites.
It is vital that you do not enter into these discussions with a defensive air. The agent will not make such requests lightly. Find an agent with whom you can establish a rapport of success, and aim high.