What I find about the wiki is that there's a lot of very frank, unconnected information that's certainly useful in its own right, but generally doesn't address most of the frequent questions such as 'how to drain a magma pipe' (just an example). On the wiki, you'd find articles about screw pumps, power, magma, and magma pipes, but would have to already know and understand how the game works to be able to put them together (plus other things, like how you would usually have to tap into a layer of the pipe that sticks out more than the one above it). Yet so many questions on the gameplay forum keep getting responses like "Try looking at the page on magma pipes. The wiki is a very valuable tool!" As a game that's about the mechanics just as much as it is the ways that these mechanics can be used together to do crazy things (which to me is the entire draw of DF), I rarely see anything about the latter. So I suppose my suggestion would be to add 'Interesting things you can do' that focuses on stuff like this in detail.
Even the stuff on the wiki that is related to using different aspects of the game together could be reworked to make more sense, offer more suggestions, and mention more ways to do things and most importantly why. The page on damming rivers has a bit on using magma, for example, that just says to pump magma into the river. No mention of how to control where it's to be pumped, nor how to get it there in the first place, etc. I try and frequent the gameplay forum as much as I can to help out when I know the answer, but I still end up writing the same responses over and over that could easily be placed on the wiki. The 'state only direct knowledge, not what to do with it' policy that the wiki seems to have is, I think, a big hindrance in new players working their way up the learning cliff.
There's a bunch more topics like this (eg. controlled, shaped cave-ins, how to build underwater structures, detailed obsidian casting (yes, regardless of having a wiki page already)) that I can't think of all at once but have crossed my mind at some point. I might have to come back and make a very rough list later. But I'm sure by now you understand what I'm getting at.