Hey Daniel,
I would say they offer a neutral benefit for the following reasons...
- Firstly, by nature sidebars are often replicated across multiple page. They are items that require high visibility and therefore can appear on all pages.
- From a usability perspective, it is good to keep consistency. Styling your H1-6 tags helps as visual aids to attract the users gaze to key parts of the content.
- If a potion of a page is duplicate content, it typically would not affect the rest of the content on the site from ranking. Although I would imagine malicious use of duplicate content could.
My preference would be to use lower Heading tags (say H4,5,6) as not to dilute the use of the primary heading tags, but ultimate this duplicated sidebar is going to offer little SEO benefit from a content perspective. Sidebars can promote other SEO benefits though such as internal linking and usability.
This can apply to the footer area as well, although I would be less inclined to use heading tags (I am sure there are exceptions)
Hope this helps,
Dan