Indeed a couple of posts made in the last few months have been prescient of serious and highly secretive information. The motivation behind such posters is likely explained below.
I think what a lot of people don't get about /pol/'s influence in the last year is it's mechanism. It is easy to browse the site as an outsider and think it is just shitposting 9000, with no real influence outside. However /pol/ unconsciously and without formal direction has an extremely effective strategy for disseminating information.
Once the essence of some information has been distilled users start disseminating it to the 'normies' via Reddit and Twitter. Twitter is where the real influence comes as they inevitably target journalists in large numbers. As most know, journalists and politicians are extremely engaged in Twitter. Stories frequently then cross the barrier into the mainstream.
Targeting of journalists and politicians, largely but not always via Twitter, is where most of the huge power is derived. People targeted don't necessarily have the internet experience to realise when these things are directed. A lot of what most of them see is a flurry of regular public concern which needs to be addressed.
When a story from /pol/ reaches the mainstream, it goes into a glorious frenzy. It is a powerful feeling when something you have created/discovered and disseminated in a 4chan thread becomes international news because of the boards collective action.
Summarised: when a very large group of people with political leanings on a story/topic informally organise, the effort can take the view mainstream. important to note is the demographic includes a diverse group of users who are highly skilled in programming, social media and politics.
edit: If I was a highly placed politician and wanted to disseminate secret information without attribution, I would run it through the tumbler that is 4chan.