I think it's more about click through rate increase with the schema.org mark up.
So, if you mark up your page, your intention is to basically provide more information when people view the search results of a search, and thus they are more likely to click through to it and visit your site because it stands out when compared to sites without the aid of schema.org mark up.
For example, if you search for a local business, a plumber for example, you'll see the results populate within a search engine.. and.. the mark up adds additional real estate to the sites listed if they are marking up the page..
People like to read reviews, so a local business should add this mark up to the review data within the site. More people are probably going to click on a plumber's website if the reviews are displayed in the search results vs a plumber who's reviews are not displayed in search results.
The schema.org sitenavigation mark up data adds the largest real estate to your listing within results, and makes your page look larger in the results and makes other pages look smaller, thus more people are visually attracted to such results due to the difference in visual size and you'll most likely see higher click through ratios with larger real estate on search results - this is something everyone desires to achieve within google results regardless of what their site is competing for.
But you probably know all this already..
So, does schema.org mark up directly add to a sites actual rank? I doubt it.
The markup is best viewed as a tool, and it simply provides more details about the result of a page if the search engine chooses to display such marked up data in it's results, which may or may not happen. You shouldn't mark up a page and expect rank increases that are going to launch you ahead of your competitors simply because your page is marked up.. even if theirs isn't.
Simply marking up your page's data isn't going to guarantee the data gets displayed in a list of search results either, but it is something you want to plan for and strive to earn, because more people are going to click on your site's results once this data is displayed.
If the page you're working on is ranking it will be more likely to display this data, and more of it.
If your serps are a fire, then schema mark up is simply fuel added to this fire - It makes your results bigger, brighter, and more likely to be visited by people who happen to be searching through your niche and your competition. Like flies on $h*t.
So your Local Business landing page most likely wants to achieve review data being displayed in results, contact information, logo, map, image. Fulfill the requirements that google wants met for the localbusiness schema.org context which you can find in their webmaster tools somewhere. Search for your competitors, look at the data that's being displayed in your niche, and try to incorporate the same, and make sure web crawlers have the ability to verify the marked up data on the page you are marking up. The google structured data testing tool can be used to see if there are any errors in your mark up, these need to be resolved if they exist as well.
Are you going to be able to include all the marked up data in your results and should you go above and beyond what actually is supported by search engines? That is to say, if you add extra mark up to your page beyond the requirements listed, don't expect these to be displayed. There is much more schema.org mark up data elements than their is actual data results that get displayed via google. Try to achieve what google lists as required input for the local business, pass the verification with the structured data testing tool, make sure the actual data is found on the page your marking up, and expect no special treatment beyond the same data items you're seeing listed with the other competitors in your niche.
