I think PR is unimportant. As you say sites with low PR can be positioned better in the serp's than high pr sites. Yes pr is related to incoming links, but that is what you need to concentrate on - incoming links. Dont worry about leaking pr away from your site or any of this type of thing.
unintentionally but fortunately for the big G, pr keeps Google on the lips of many, many webmasters and people in the world of seo. It is a "front" for what is really important in optimisation. Dont get carried away with pr. Remain gaining quality links and yes your pr will increase, but there is no need to keep a careful eye on your pr. If that is what you are interested, yes it will increase over time BUT surely serp's are far more important?