Is it better to spend time on your most successful traffic-generating links to make them more effective, or work on getting more links in hopes of getting another successful one? What balance/mixture do you use?
Mayby You should try article marketing? It's the best and most powerfull way of getting strong backlinks.
Article marketing it's good only when it comes to getting hits from those article sites, or when you get listed on se's with your articles on those domains. For link building I would recommend getting tons of links to your site, the more the better.
I spend 15 minutes a day submitting to web directories. Using those links to target specific keywords and pages on my sites that I want boosted. Then I spend 45 minutes researching sites in an effort to get links from places that will give me traffic. I get a lot more links in the first 15 minutes...but the ones I get in the last 45 minutes really pay off in traffic both from the other site and the SERPs. For me the combination of the two has got me #1 Google rankings for fairly competitive terms. Oh, I forgot one more important thing. Spend the rest of your day building content that other people will want to link to or you'll waste the first hour of your day.