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Maybe not in ranking per se. But if you are signed in as you search, and your google plus profile happened to somehow interacted or be connected-with the person (especially if he is really a well known and well connected ie a lot of people have circled him/her on G+); for those signed in users the article might have showed up on the first page (lets say) and with no authorship or someone else might not even show up. With this in mind I would keep the author that has the most influences or people that have circled him, or that has the most activity on his/her Google+ network. Again Google is saying one thing, but with the move of making the search more social this is not unlikely. This also in Google's eyes may not be a pure "ranking" process but more related to "displaying relevant info" from your friends on the G+ network. Just some thoughts

Thanks Axial, I'm not convinced it matters much if Google crawls deep pages they wouldn't find through organic links. If the pages aren't linked to they won't have any link juice and therefore won't rank well in SERPs. The link about using site maps for canonical URLs says or implies you should only put your most important URLs in the sitemap. The sitemap tools I've seen tend to take a kitchen sink approach, which is needed if you are using it to try to get a deeper crawl. Plus there's no way (I see) in a sitemap to specify that page A is the canonical of page B. They simply suggest telling Google about page A (and not page B) in the hopes page A will get more weight than page B. A canonical meta tag on page B pointing to page A is obviously a much better way to deal with canonicals. Image and video site maps are potentially valuable. I am asking specifically about site maps for pages. Specifying related content for a given URL, such as different languages, is indeed useful and not something I was aware of. But it is not applicable on most sites and not used on most site maps.

That sounds like you have a site that people value. I would use the rotators.  The number who return might move up. The site where I use the most rotators has lots people who visit daily to get news. I have a retail site with daily content rotation that has people who return a couple times per month. For a while we were offering special price items that changed daily on one site.  That was bringing a nice number of people to the site to see "what is on sale today"... but we quit doing that because people were calling us wanting a special price from last week.