If you believe in link-juice theory, then you must concede that
PR is all important when building backlinks.
PR is a measure of this link juice, and if a page has PR0 or
PR n/a, it means that the page has near zero link juice to give your site if you get your link on there. PR2 is worth many PR1, PR3 is worth many PR2 and so-on.
This is why, for reasons of time efficiency more than anything else, I tend not to look at anything below PR3. And I consider an hour spent finding one good PR5 backlink much better than getting 100 PR0 backlinks in that same timeframe.
Many of you will be thinking about the authority effect playing a positive role even on
PR n/a links. I don't know how powerful it is or if it exists but in all my backlinking experiments I have seen scant evidence of it. For example, I hit one of my blogs with a PR7 link from NASA.gov, and a PR7 from Yale.edu, it hasn't helped much at all. Although maybe that was overkill
So, in answer to the question, PR0 backlinks are not worthwhile because they are not time efficient ways of boosting SERP position. I advise you to look for fewer, higher
PR pages (not just domains - for a good backlink, the page itself needs the high PR). I have had great success using these sorts of backlinks.