Q1: For me, it depends on the competitiveness of my keyword. I only do enough link building necessary to get to certain level, and that's different for each keyword/niche. I've found these type of links will only get me so far, then I have to begin doing other SEO tactics like videos, press releases, front page high PR links, etc. (most of the time); sometimes it's such a low competition keyword that I can rank without all the extra, but that's rare).
Q2: It's the different IP's and the page rank that give the link juice.
Personally, my strategy has changed in the last 6 months. With the advent of so many automatic link building software/services, I load up 5-10,000 auto-approve links and fre away first thing. I use a shotgun, then a rifle.