How important is Readability i.e Flesch/Flesch–Kincaid Readability Tests

Question

It has been my understanding for some time that Google uses readability tests similar to Flesch.

While I understand readability is important for user experience I'd like to know the importance for SEO/User experience. For the community of Pro Webmasters who know me, I'm always the first to scream out write for your audience not the search engines. However, you may consider your writing good while your audience doesn't, the search engines doesn't, etc. I'm a true believer that you a should always get someone else to proof read your stuff before you hit the good old submit button, however this is not always possible, especially for those who operate a one man army.

Is Flesch or anything similar to be taken seriously for both user experience and SEO. I appreciate this question may appear opinionated on the surface, however I'm not looking for 'I think this or that', preferably I'd like well constructed answers citing Google or anyone else highly respected in terms of readability importance and how to directly affects SEO.

Answer 1

We are building a ranking correlation database at Corporate SEO that scans tens of thousands of pages per day, assessing over 60 different metrics such as PR, CF, TF, DA, PA, mozTrust, Power*Trust, LIS, etc, including the various readability metrics, to identify the best combination of metrics to predict ranking for various categories of interest.

The reasons we are including readability metrics are:

1. They're easy to calculate, so Google will most likely be doing so.
2. A respected SEO peer swears that a Flesch Reading Ease score of >70 works wonders for rankings.
3. SEO guru Yoast considers it important enough to include in his renown WordPress plugin.
4. Badly spun text often fails these tests miserably.