Welcome to the Q&A Forum

Marisa,

Yes, it is possible for an internal page to have higher PR than the hompage.  Sometimes a site will host a viral piece of content (infographic, quiz or an awesome blog post etc..) that will dramatically increase that pages PR.  This is not a bad thing, but can be a very good asset.

On to your last question, depending on how you have your internal link structured the link juice coming into the site will help all your pages rank more aggressively in the SERPs.  ingeneral onpage SEO will only help the page that you are optimizing ranking more aggressively.  However, if you are optimizing your internal links to other pages, this will help those pages rank better too.  So in short, it depends on what you are doing.  If you are just optimizing the Title tag, meta description, H1 tag and keywords on the page. You are really only helping that page rank better.  However, if you are linking to other pages from within the body copy and optimizing your internal links to pass more juice.  That will help all your pages rank better.

Remember that google doesn't rank site, it ranks pages.

I hope this helps.

Thanks,

Jason

Ingeneral (I have not seen your site or know what problems it might have), if your site was hit by panda then adding great content to all your pages would probably help your homepage rank better for your targeted keywords.  However, I don't know if you are having a panda problem or just need to do more link building to your homepage and optimize it.  A panda penalty can reduce the rankings of all the pages on a site.

Also, adding quality content that helps the user is never the wrong choice to make.  However, if you are trying to get your homepage ranking better for a specific phrase and you don't have penalties/filters on the page.  Then I would probably focus on link building and doing on page SEO for that page and funneling the link juice from the other high PR pages on the site to my homepage more efficiently.

I hope this helps.

Thanks,

Jason