The head part is the most important part. You should have your keyphrase in <h1> </h1> brackets etc etc
Of course, they are obviously importance in SEO point of view. However, you must jam-pack your header with keywords more than necessary. Also, just a single keyword in footer will do. Hope this would help.
header footer main content its all part of the page, no part is more important than the next. header controls page title and meta content controls the keyword rich article footer controls navigation links to extra pages (especially important for real users)
Footer have less weight then content part, but have some value. And header is more important. Can't measure exactly but you should think more what's going in header then in footer part.
This elements all play there parts. Header should define the niche/keywords you are tarketing Content should talk about those keywords Footer should have a second menu(if you already had one), link to Contact, FAQ, ToS etc.