Page rank is a very big topic and has been covered by all the experts. I have read reports that tell you it’s not that important, but I say it is. If you want quality traffic delivered to your website then it’s something you should strive to improve.
I have one site that I have been working on for a couple of years and at one point I had a 4 rank, but recently I moved that site and had a few set backs with setting it back up. I have learned not to change the page names and move things around without using 301 directs, but even that might not have helped.
It really bothers me to go to that site and see no page rank now. I have to start all over again. At least my other sites stayed the same this time. I try to maintain and keep them updated. I do not like to lose rank. I like getting the free traffic.
The structure of your site is important to keep and maintain your rank. So if your thinking about redoing your site get advise from an expert. Also I am now concerned with links. I think it is better for your site rank to have quality instead of quantity. I am sure Google checks where your links are coming from. Do you know which sites are linking to you ?