Yes! Absolutely. Without question. Regardless of how good your writing is, you need a professional editor to work with you before you publish.
Think of it this way: your editor is a black box through which you send your manuscript–line by line. She will tell you whether the ideas, thoughts, connections and emotion you intended to produce in the reader’s mind when you crafted that sentence is what you actually produced.
Meghan Ward of the Grotto writing consortium in San Francisco has just posted a terrific little piece on tips for hiring a freelance editor–including costs associated with a professional edit. Highly recommended.