Even though stupid people sometimes get things right, and smart people sometimes get things wrong, that doesn't say anything about how often they do so (comparatively). You can't use those rare cases to negate the 'assumption' that intelligence aids correct judgements. It just means that intelligence is not a 100% guarantee of correctness - but we knew that anyway. As it stands, the usefulness of different aspects of intelligence - reasoning, analytical ability and so on - in assessing probablities and making judgements is fairly obvious.
Also, even if the personal beliefs of one individual don't serve as very strong evidence, a large-scale trend towards more intelligent people favouring one side of the argument should be taken into account. It's not so much evidence in itself as meta-evidence that a) other people who may know things you don't, tend to favour one option; and b) other people with the same knowledge as you, but better processing capabilities, tend to favour that option. With more complex issues which you may not have much personal experience of, this could be a rather substantial factor in your probability assessment.
I should also point out that it's intelligence, not stupidity, that is important. Intelligent supporters of a view can be taken as reasonably strong evidence, as seen above. Stupid people have less intelligence, therefore their view should be weaker evidence - but even a stupid person supporting something INCREASES the probability that that view is correct, albeit by such a small amount that it can almost be ignored in favour of assessing what smart people think.
Of course, then there's the worldview difference to consider, and the fact that even if they can make a better decision than you, their "better" option may not lead to a more desirable world from your perspective.
My school doesn't offer IB, but there's an ToK equivalent under our CIE (Cambridge International Examinations) course called Thinking Skills. It's a bit more focused than ToK - it doesn't try to teach students how to think, but instead focuses more on specific thinking techniques. For example, there's an emphasis on deconstructing arguments, analysing essays, and identifying logical reasoning. While that's not quite as useful as what well-applied ToK sounds like, it's probably a bit more realistic in terms of ability to convey information to pupils - it's still very much an assessed subject. There's also a multichoice problem-solving section, although I'm not sure to what extent this can be taught - it seems to measure inherent logical skills and IQ as much as anything else.