My bias is yes, you do for sure.
An agent reacted to this article about whether one needs an agent or not.
Her reaction is here.
My thought is that I don’t agree with two parts of the article.
One part says, “MYTH: You will make more money-and faster-using an agent. REALITY: Strike one against that myth is the fact that an agent will take 15% off the top of anything you earn. Strike two is that editors really don’t have a prejudice against unrepresented authors. They’re just looking for the best stories they can find. (Some larger publishing houses have instituted a policy of reviewing only those submissions sent by agents, so check in advance if you’re representing yourself.) Strike three is the simple truth that it takes a long time and a lot of hard work for anyone-represented or not-to make substantial money as a children’s book author.”
My take: In my experience, many editors don’t take unagented submissions. (This is especially true when you talk about books for adults.) And if editors do take unagented submissions, they get read last, behind agented ones. And most agents are able to take the first offer and negotiate it up enough to at least cover their 15% - something that the average author would have a hard time with.
Another section says, “MYTH: An agent can make you a better writer or illustrator. REALITY: If your story has been turned down by 25 publishing houses, representation will not make the story more salable, or appear to be better than it is. Only your own hard work will improve your skills-and your chances of success.”
My take: The myth and reality address different issues. The reality is about a specific story, while the myth is about an author. My agent has made me a better writer with her feedback. Sure, I have to do the work, but she points me in the right direction with specific feedback. And that’s priceless.