Throwing in my 2cents here...
I used to be a strict primary position, cyclecraft kinda guy. It didn't work out too well for me, in fact, I ended up taking 2+ months off cycling because I was getting so stressed.
Now I adopt a totally different approach.
Instead of worrying about what cars are going to do around me, I made my primary concern "enjoying the ride". I, you, we, already know how to deal with motons - otherwise we wouldn't be riding. Since making the mental leap from "I can't credit the stupidity! The cu*t just passed me 10m before a red traffic light! What did that going them?" and equating that with "Meh, so they go past, what's it going to cost me?" I am a hell of a lot happier.
That's not to say I don't assert my right to the road, but I do it in a different way. A calmer, more hippie way. When I need space I take it, when I don't, I don't make a fuss about asserting my position, and ride kinda closeish to the left.
Probably what has made the biggest difference to me is taking more time at junctions. Sitting 2-4 cars back in the queue, and not using my ability to filter at all opportunities.