Is there any value from backlink from high-PR site, if the actual link page does not carry any? For example PR of root of the site is 6. PR of links.php is 0. is there any benefit of a link from links.php? (besides "just a link" value)
Yes. I think the home page PR of the site providing the link is calculated, even if it's a small amount.
Basically we need to have links from all pr category not only pr5 and above or something of that kind.