Also, one of my favourite tropes is "Dumbass Has A Point" where a normally-stupid character makes a logical or convincing argument to the astonishment of his smarter friends.

A prime example of this is the Breaking Bad episode where the police get a laptop that would prove their guilt, with Walter and Mike debating on how to handle it, debating about whether to skip town or attack the police station with a bomb. Whose plan do they go with? Jessie's, who points out that they can fry the computer with an electromagnet.

Also, in the Golden Girls, Rose is the resident ditz of the household and is frequently played off as a moron since she didn't graduate high school. However, she turns out to have read the scientific journal used by professional psychologists to diagnose mental disorders back-to-back and can accurately diagnose mental disorders (calling someone out for being detached from reality and calling Blanche a hypersexual bitch, but the last one was an insult) and when Dorothy has a gambling problem, manipulates her int feeling guilty as a means of treating the problem.

Edit: Also, look at Danganronpa. When trying to figure out who the killer is and at an impasse, the dumber characters spouting shit off randomly will often be correct.

For example, Akane in the second game is frustrated when they realise there's no way for them to figure out how the killer could've moved around during a blackout without any kind of hints or clues, so she frustratingly shouted out, "What if the killer >!used a light?!!<.

To her surprise, main character Hajime outright confirms that yes, this is indeed what the killer did. >!The killer was never in the room in the first place and by using a smaller light, was able to sneak around outside the room the murder took place in.!<

Also, Yasuhiro in the first game, who is so utterly stupid that he was held back in school multiple times (I think it's mentioned he's two-to-three years older than the others who are all part of the same class in high school) and his stupidity is repeatedly highlighted. But he also points out one of the biggest flaws in the third case, which he's the main suspect in and needs to prove his innocence.

He rightfully points out that the killer was attacking everyone outside of the presumed order by citing the fact that the murder weapons were taken from a fictitious fighting robot anime, which required attacking people in turn with an escalating sequence of hammers (Justice Hammer 1, Justice Hammer 2, etc.) Yasuhiro points out that the killer could've just attacked with the hammers out of order, citing the fact that they already found the third hammer; the killer would've had to have stolen it from the other survivors, attacked someone with it then put it back where they found it, which was too risky.