Very common Tactic.  I would say use your resources building great content on your main site, and you will see a better return.  The question you are asking really comes down to a point of view, and then math.

A bunch of sites, with little or no juice, will help a little.  A bunch of links back from Blogs. Sites, and social media will pay off big time if you can create the interesting content. Interesting is:

"something that concerns, involves, draws the attention of, or arouses the curiosity of a person"

So I would ask this question.  What is it you can do with the current web site that will create Interest.

Mine too!

Trying to force a search engine into indexing a page is a losing tactic. Having been down the social media profiles path, in my opinion, (and based on our limited research) it's far better to focus your energy on a few high profile social sites (Twitter, face book, linked in)  and do so from the non SEO approach. Give great information, interact,  and meet interesting people and businesses.  The SEO effect will follow.

Having your clients Face book comments shared is far more important than having 250 social profiles.  Let's face it, if you can buy 100's of social media profiles for $5.00  how valuable can that really be?

One of our major challenges with clients is convincing them that the easy road in SEO  may head up for a while, but always seems to end with a long slow and ugly decline. (a mountain road metaphor)

Go for Quality!  Think like there is no Google or Bing and your SEOo will produce better and longer term results.

While I have seen temporary rating boasts with social profiles,  unless the account is used as intended,  and grown, those ratings disappear pretty fast.