In my book (figuratively and literally), good copyediting is invaluable.
I read over my work a dozen times at least, and catch things every time. But I still need a good, professional, experienced copyeditor to read my writing before it's published.
After I wrote my novel "Firefly Island", I must have read it a good twenty times. I then had about twenty beta readers read it. After I sold it, an editor at my publishing house (Five Star) worked with me to improve it. Finally, a Five Star copyeditor reviewed it.
I wouldn't have published the novel any sooner.
If you're an indie author, and don't want to pay to hire a professional copyeditor, I suggest at the very least running your novel several times through a good writers' workshop. Then see if you can find a local English or journalism student; maybe they'll copyedit your book for cheap (or free).
I love indie authors and love supporting them. One reason I love ebooks is because it gives indie authors a voice and audience. But indie novels should strive to be of equal -- or superior -- quality to the books from the pro publishers. There's NO excuse for publishing a novel full of typos and grammatical errors. If you're going indie, find a good workshop, find cheap copyeditors, find an English teacher or student to read your book... and revise revise revise.
It's worth it!
Daniel
Firefly Island, a fantasy novel
http://www.DanielArenson.com