What I don't get, is that people are selling links from deep inner pages of high PR sites, which have PR of zero on the inner page. Do those help? I mean, you can get a PR 10 inner page do follow link from Google, or NASA, or whatever, but those inner page have no page rank. Are those of any value? If the inner page has no page rank, but on a high page rank domain? If that works, you can probably use software like xumer to create literally millions of do follow backlinks from those sites? If it doesn't work, why are people paying money for those links?
for sure it helps. specially if the sites are within your niche. high PR sites usually have higher authority (in general given that the PR is natural. you can buy whole bunch of high PR links to boost your PR which doesn;t mean that you got an authority site.). if you get a backlink form inner pages even on a new page which has PR zero, you are still getting a backlink form a authority domain PR0 inner page on high PR site will not always be PR0. the main domain will transfer some PR to the inner pages over time so the inner page PR will surely increase in the future.
Yeah High PR sites transfer good juice to their inner pages thus a link from a PR 0 page on high PR domain is worth more than any old link from a PR 0 site. Now if the site is relative to your niche or area of business then this will bode well. However, I will take a link from a high PR domain or page in an unrelated niche over a lower PR Domain or page in a related area.
Providing the site is of high quality, as well as "trusted" and "related" to your site, if nothing else, trust transfers... This alone makes it worthwhile - generally speaking.