My website a Legal Search Engine lawmirror.com and there are about 600k records available online. Currently using xHTML5 and on some pages Microdata tags. Same record appears many times on different keywords search. Google already crawled about 1000K pages but traffic is very low. Does using the RDFa, improve the ranking and traffic.
No using RDFa, microdata, richsnippets, and HTML5 does not help your rankings in search engines. If you use Google rich snippet testing tool they'll actually tell you if a page will potentially appear in search results with rich snippets or not. For example a page using hCard but with a lot of other content on that page google may determine the main relevancy of the page doesn't support using hCard in search results. You can have the most well validated pages, using the latest schemeas and even the ones in beta, all that will not help you rank higher.