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Your first link didn't work.

Links from these shallow sites probably won't help much for passing link juice (low authority presumably) but if they're getting traffic then you might want those visitors to see your flagship brand where you have the bulk of your content.  In that case, it would benefit the visitor and therefore would be worth doing.

As always be careful with linking to your flag ship site if the shallow sites are linked to by spammy sites.  It seems to already doing pretty well so taking chances for minimal benefit probably wouldn't be worth it.

Branding and visibility issues aside, from a pure link standpoint those links don't count (or shouldn't per Google).  Google wants affiliate links to be nofollow since they're advertorial (Matt Cutts on the matter - <a>http://www.youtube.com/watch?v=1SmlsfSqmOw</a>).  Cutts also says affiliate links should be disclosed adequately.  Now on the other hand, you're right that these links are benefiting a company that has these relationships set up.  I'm sure they're getting visibility, traffic, and ultimately sales.

The blog link you mentioned will provide diminishing returns as the initial link you get from a domain is the most helpful and each subsequent link from the same domain is worth less and less.

The forum does indeed sound sketchy if there are links to unrelated sites.  You are in a good position because your competitors link profile doesn't look great.

I also look at the proportion of DA and PA to number of RDs.  The lower the ratio (more RDs) the worse the link profile is.  For instance a site that has a DA of 30 with 15 unique domains has a great ratio.  A site with DA 30 and 500 RDs has a much worse link profile.

This particular site is not impressive.

Eric, I'm really confused.  AddThis automatically adds a tracking code each time the page is loaded.  If you click refresh you'll notice that the code changes.

What do you mean the URL isn't being indexed?  Google is ranking that page for the keyword.  And I might be mistaken but my understanding is that Google disregards everything after the "#" so there shouldn't be a duplicate content issue.