Hell a lot of low quality submissions and upon analyzing I fell PR NA to PR 3 are mostly useless websites. However there are some exemptions. But the time to find those gems are very much high given the fact that there are hundreds of low PR websites to review. On the other side PR 5 and above websites are mostly established and quality websites. Again exceptions are there, but this can be easily handled as the volume of high PR submissions are less. So, my question - Is it better to accept websites only above a specific PR? I read The "YOU should NOT start a web directory" List post and one of the points was not to do this.
PR is a flimsy indicator of quality. Yes sites/pages (or is that domains/pages) are generally more established, but using it as an indicator stops you from a greater depth of research on a site. A large number of websites are built upon the PR acquired via a dropped domain. Then legitimate looking, but fake, websites are built upon this in order to sell using the PR as leverage. A whole industry revolves around this sort of stuff. So whilst it CAN indicate quality, and can be used like Alexa for a quick take on things, PR is a highly flawed model - because it is very easily manipulated; the manipulation is wholesale and widespread; and the manipulation is totally unpoliced (i.e. the worst offenders never get banned/docked/penalised despite being reported). Forget about PR. Each site's content should be reviewed on its own merits, not a silly little number that Google totally lost control of many years ago.
Although the PR is decied on the quality of the website.We also need to submite the site to the low PR
You should take decision based on the quality and relevancy of a website rather than PR. e.g. local business websites normally fall into below PR 2 but may be worth including in a directory.
IMHO no don't use any metrics such as pr, alexa, hosting etc. when you review a site. I'd advise to turn off the free subs which seems to be your problem and spend the time populating your directory yourself. As a parallel example I see many blog directories not accepting sites hosted by 3rd parties such as blogger, yet there's some great scientific blogs hosted with these people and these are real bloggers too busy with their work to worry about their url.
All links should be manually reviewed however if your lazy or just receiving to many links a day you could auto approve PR5+ websites. Any website that has a PR5+ is established. PR0 links could also be dropped as they are typically new and have had no effort into link building since PR1 is easy to achieve. If you are lazy this leaves you with only PR1->PR4 links to approve manually.