I agree as far as the “Sexual Harassment” suits. Statute of limitations.
But....
This new chick though, could destroy all credibility for Cain.
He has the money to sue her to oblivion and prove he did not have an affair. The man has money, lots and lots of expendable income from years of success. He doesn’t need to recoup anything from her financially (and would never get it anyway, as you mentioned). His lawyers could handle this while he continues to campaign. Matter of fact, if he went so far as to state that this was his intention; I would be willing to bet if this is a lie, she would back WAY off and right quick!
I feel he needs to do this because all this negative press is not only destroying his campaign, it could be destroying his future outside of politics.
While he continues to deny it, people continue to question him.
If it was me, I would do exactly that, sue for defamation. however a lawsuit would certainly become media circus, and make it impossible to campaign. So I suppose Cain is doing the next best thing, appear on prominent shows and make his statement such as on Cavuto today.