I read and also suggested by pro SEO tools that Keyword prominence matters a lot, is there any substantial evidence that Google or any other search engines give importance to it ?
Keyword presence is more important than prominence. Sometimes prominence of keyword works against the website too, keep it user-friendly and use keywords only if they are absolute necessity - unnecessary use of keywords will results in poor rankings of your website. any more questions - do post here, i will be happy to answer !
Forget this thing just try to make your content unique, fresh & quality one. If you have all these things in your web page content then you don't have need to play your content..........................