As with any industry in the world, publishing is ever-evolving and changing too. Cover design is no exception. What was ‘current’ cover design 2 years ago, is not so ‘current’ anymore.
To keep your already published book relevant, make it even more competitive by giving the cover a ‘facelift’. Hey, even the ‘Big Authors’ have their covers revamped to keep up!
Stay in the game, keep your cover current.
Not sure your cover is cutting it? Read this article by JH that appeared on www.indieauthornews.com
http://jhillustration.wordpress.com/2012/10/15/why-you-need-professional-cover-art-bad-cover-bad-sales/
JH Illustration 
Nice change. That’s a huge difference.