I can't even understand what he means... Well, pr is just a pr... I am not saying that is not important but i think one should need to focus to build more links for their site. As for PR, you will be needing this for link trading. Again it doesn't mean that you should link trade to other sites but more sites will be willing to link on your site without linking back on their site if they saw that your site has a high pr.
well if the site's Page Rank is dropped you could get new backlinks with higher PR and at the next update you could get decent Page Rank again.
If you had PR previously and you are now PR0 or the PR bar is greyed out, then you will have a tough time getting that PR back. It is true that PR itself is not important, but it also equates to trust from Google. You have to remove anything spammy from your website and figure out if there is anything else that could cause a penalty. Then once you think everything is fixed, you submit a reinclusion request with Google explaining the situation.
PR is a handy 'dummys guide' way of representing how important google thinks your site is. What you are saying is like saying 'forget the expression "fine weather". Concentrate on wind speed, temperature and relative humidity". Have a nice day.