Google calculates to different values and both are important. There's the importance of the site, primarily measured by PR, and then there's relevance for a specific query. Neither "link juice" (actual PR) nor domain history help at all with
relevance, with a specific query.
www.whitehouse.gov has great PR and such and Google likes that site. Yet it is nowhere to be found when I search for "competence". Why? because though it's a good site, there's no "competence" there.
If you focus just on PR, you'll be in the same boat - think your site isn't relevant for any search, so it won't be returned at all and your PR won't matter. That said, that doesn't mean I'm saying you should keyword stuff your description, title, etc, or H1 tags. As Kelli said, those determine what the user sees, so making those attractive to humans may get more clicks then placing a few spots higher.
As far as heading tags and Google, see how we basically get five to seven listings, depending on the search term:
Google X 7
Smaller sublistings
The URLs Google links and the titles they use happen to be the links in our H2s. besides Google, using heading tags is good for humans, like those on more limited mobile devices or using screenreaders or custom CSS due to reduced eyesight, as well as other automated systems. So use heading tags, but don't stuff them.
PS - I'm not a "Google whore" and these days I'm not an SEO expert, though I was once. These days I'm just a guy who has been getting some SE traffic for over fifteen years without having to spend a lot of time and effort re-doing things.