Well, if URL.com is your domain, you're sitting in high cotton.
I assume though that URL.com is not your domain and you are just using it as an example domain. That said, it's very tough to estimate what effect a single folder is going to have on your PR. Traffic-wise, an additional folder is probably not going to make any sort of difference. Most likely it won't make a difference in your PR either unless it is laser targeted on your niche and is designed as an "authority" type of page / section. Even then, it's going to take time for the SE's to notice and reward you for this.
Page rank is 100% determined by incoming links to your page. Number of pages or content have zero direct affect (although good content can increase the chances people will want to link to your site) - so it would have no affect on PR.
Adding a blog and forum is no guarantee that it will get any traffic. The directory is the least likely to increase traffic imo.