When you obtain say a page rank of 3, does it get harder and harder to gain a page rank of 4 and 5, etc? I know it has a lot to do with your content, so does a mass amount of content do the trick?
If you continuously improved your content and gather strong backlinks, Google will rank your site accordingly. It means to gain higher PR, you have t work harder on your site's reputation and authority..
If u want increase ur PR. U have to concentrate on improved and unique content. You have to work on more on-page activities, quality content updation and continuously creating quality and high PR back links. This all helps u to increase ur PR of the site.
Yes getting a PR after 3 is somewhat difficult. but if you build high quality back links from theme based sites, or from some authority sites then you can easily do this task. Domain age also plays a major role in getting a high PR.
Quantity does not matter the thing that matter is Quality. So instead of running behind the quantity improve your quality and try to satisfy users that visit your site. User satisfaction plays an import role in SEO.
Google assigns you PR based on reputation and quality of your backlinks. Get more ‘quality backlinks’ and improve your PR. Although I never bother about PR of my web pages as they are less important in adjudging your site’s performance... It prefer to focus on other metrics like SERP rankings, traffic and conversion.