@JesterMagic, by now you've gone through all this but as my 2¢ - social pages are good for SEO if you USE them and it comes in a few forms; as a disclaimer: SEO here means getting involved with real people. I do the PAGE pages (not personal profiles) on all social networks per site, no mixing there. Before anyone criticizes the effort about to be described, the outcome should be that value is added to the website by the webmaster acting AS the website socially. Not all sites need it like this.
You can't be your only fan/follower reposting your own stuff from your personal profiles and other pages; you have to get engagement working for you and that means
- learning those different audiences
- "making friends" that are actually interesting to your niche, receptive to your messages and potential promoters (and maybe something to promote for others)
- sharing posts and information that are interesting and not always promotional, etc.
No lie, it's work to deal with it that way and hard for me to divide time finding something of quality to "share" per site (most Pages don't get the attention the website deserves). Some folks automate the process but I find doing it manually lets me see the incoming stream of people in #2 because they might offer some news or something you want to pass along.
Is all that necessary? No. Not all social sites are useful. To me Pinterest is pretty useless and pointless without real interaction but even there I'll post things that the Website's audience might find interesting including photos from some articles from each website.
Blah, blah, that's my 2¢.
EDIT: maybe this is more helpful: Our busiest site has a particular audience it attracts, about 2% of those visitors I want to work with on a slightly different level. Using social networks the SITE is able to reach out to those types of people directly who in turn interact with more people like them both socially and in their physical world.