Meanwhile, my plan of attack is to get an exotic piece of armour. And a legendary helm, which I will be able to do next week after the mark reset (it'll be the Dustwalker one to complete the set).
I might have a problem, I went to do some more patrol missions on Earth so I'd be able to hit Vanguard rank 6 and I ended up finding - honestly without much hunting - 49 more spinmetal, so I'm on 251 now. I'm also only 250xp away from Cryptarch rank 16, I've pretty much been ranking that up twice a day for the past three days. What that says about me, I don't know, I don't think I want to know either.
For anyone wanting to boost their Vanguard rank quickly, you might want to watch this:
In my experience what really slows it down is the delay between completing a mission and the next one appearing so to have three people covering most of the map would speed things up a lot. One thing I want to test is if I'm in, say, The Divide and someone else in the same fireteam is farming the loot cave, will engrams that drop there - that I never see or go near - go to my postmaster when we leave? I suppose they wouldn't but it'd be cool if they did.