I can provide you with a little anecdote but I think internal linking is a reasonably large factor, especially from the home page.
So I have a page, 3 levels deep, absolute tail end of my site and exists exclusively to catch the keyword it's targeting; doesn't provide any information you can't get elsewhere on the site, doesn't have any exclusive offers, just another page on the site.
So I build a few links into this page, nothing exciting; articles, links from my blog posts, manage to find a couple of websites about the topic, but after 3 months, nothing, top 50 ranking (from 120 or so) but not that great. However one day I get a conversion from it, so I decide I'm going to give it a little push and link to it with the main keyword from the homepage.
Boom! Next day, 7th.
The homepage itself isn't that powerful, very low page rank, very few links coming in and there's already about 100 links on it between the nav and the other editorial style links. It's not that the page I linked to wasn't being crawled or indexed but putting a link in from the homepage instantly boosted it.
2 months later the page still fluctuates within the top 10, but I have been building more links into it.
So, flush with this new success I decide to test it on another, very similar, site. Same sort of page, same sort of keyword, same sort of site structure. Difference this time is that I'm not building links to the page in question.
Keyword isn't top hundred so I put the link in from the home page.
Boom! Top 80.
Alright, not as good but a definite twitch. I figure that it's not quite the magic bullet I thought it was (and realistically I can't link to every page from my home page anyway) and haven't really revisited what would happen if I did build links to that page (and a few more to the homepage).
So, anecdotally, internal linking from recent pages and small time link building doesn't do much. Linking from the homepage is a big signal that a page is important. Without external links your internal linking (on a small / low DA website) isn't going to rank you.
I'm going to say it's closer to 20/80 though.