Str82u - 1:35 am on Apr 14, 2013 (gmt 0)
Sounds like you're contradiciting yourself, "say we have identical content and links into....(...has unrelated content and links...)".
say we have identical content and links into a new site and on our current site (which effectively has unrelated content and links but the same target audience). I wonder which option would be ranked better?
If I understood you, you also have to include the possibility that both might fail. To some degree you can get away with using the duplicate content but in the same way you would reuse data for a on-site search function, not entire pages of content, just bits on it.
If you're gonna split, split big.
@TOI - the last one "One would be socially interactive" - Indeed.