Does this Schema.org markup mean your sitelinks from your nav are shown in Google? Or is this completely unrelated?
Google lists their Google Search features that make use of Schema.org. Currently there doesn’t seem to be a feature for which Schema.org’s
SiteNavigationElement type is recommended/required. This doesn’t necessarily mean that Google doesn’t make use of it, but if so, it’s undocumented.
While it’s typically preferable to provide Schema.org structured data even if Google doesn’t consume it, I think it’s not worth using any of the
WebPageElement types (which includes
SiteNavigationElement), unless in special cases (where you know that you need them).