So I would have to say that Yichus is a plus only if the descendants have absorbed the traits of their ancestors.
That seems to be what many posters are saying.
The question therefore is, so then what does the yichus do? If all you are is what you are anyway, then what is the point of the yichus?
You could say it helped you get there, and that is fine and nice. But once you are meeting someone to marry them, you pretty much know who they are anyway.