I've been to some forums that believe PR is the only thing worthy out there. They're entire study is to see how high they can get their PR.
I believe PR is good when you're trying to sell ads on your site to others etc., but not so sure it means anything beyond that.
In my opinion, it's best to work all areas. But don't forget the other PR that is just as important if not more. I'm talking about Public Relations. If you're wanting to get people to your site, relying on only the search engines, while neglecting other methods is not the best approach. Search engines work on text and mathematics. While it's true you can work to have advantage in this area, if you're wanting to drive traffic to your site, remember to you have other options like promoting it yourself. I have a site that went from 0 - 2 in a short period of time. I think it happened because somebody who has some sites that are higher in pagerank linked back to mine. However, I don't get nearly the traffic on that site as I do on another site that I just launched that has zero page rank today. I manage another site that has zero PR, yet is first in search, that the owner enjoys orders frequently from that site.
I think the best approach is to build a site that is simple, build up a client base, build things into it like a forum where people will come back and content is being created. It may take time, but in the long run, it will get indexed higher. I share the opinion of kroniczero, that indexing is more important. But having a higher PR, it helps you when you want to sell ads, links, or such on your site.