Does Having a Book Series Made Into a TV Show Effect an Author's Work?

Or perhaps the better question is, should a TV series be produced when it's based on a book series that hasn't yet ended?

I got to thinking, after reviewing Charlaine Harris's Deadlocked, that the books have gone noticeably downhill since the True Blood debuted. Coincidence? Maybe, but it's well known that Harris watches the show and I feel it has effected her work. I'm not saying it's her fault. How difficult it must be to keep your versions of the characters firmly as you've always written them when you see them taking decidedly different roads every week.

Take Tara, for instance. In the books, she's married with twins, but on True Blood, she's a baby vamp. Seeing her in that light, I know I would want to maybe give her a little more edge in the books, knowing her character could own it. And I can totally see how that could happen subconsciously when sitting down to write the next book after watching an episode. I use Tara as an extreme example being that the versions of her character have differed wildly from the start.

 She ain't nobody's baby mama now

On the other hand, I have never noticed Robert Kirkman be even slightly influenced by The Walking Dead show. Is that because he was always working in a visual medium, as the story began as comic books? Or maybe because his world had evolved so many times over so many issues, that he's too far ahead in the story for the TV show to be relevant to his current work? Or, most likely, by the time the show has gotten around to focusing on a Kirkman created character, he or she has already been long dead in the comic books.

TV shows based on books have to expand the worlds they are based on in order to provide enough material to work with in the long-term. I have yet to see a TV show that can work without creating at least a few show-based characters and changing the plot up at least a little bit. It's understandable, and usually works. What would The Walking Dead be without Daryl Dixon? But it doesn't always work. I was prepared to love The Secret Circle, but so many characters were missing that I couldn't get into it.

I chose to believe that Daryl just couldn't be contained by the page

Having your book series made into a TV show must be an exciting thing for an author. It benefits the author on many levels, not only monetarily, but also it brings in new readers to both that series and any others the author has written or may write in the future. It's an instant fan base boost.I also think it sets the author up to walk a hard line. An unforgiving one. Because long-time hardcore fans do not like their books series messed with by anyone - especially the author.

Am I crazy here? Have you noticed a series decline after it's been produced as a TV show? Or can you think of a series that has gotten better, maybe even revitalized, by its new show fanbase?