Thanks for all the replies to this. It's taken me a while to understand the various responses I got to this idea but it's gradually become a bit clearer. It seems that there are actually several possible Pd wikis that could be made or combined:
A wiki of Pd objects - a sort of in-depth illustrated help with tips and examples for every object and external
A wiki of Pd methods and applications - how to use Pd; e.g. handling midi, random functions, FFT, etc
A wiki of Pd resources, links, and examples - a guide to what is available online, Pd tutorials, instruments - a kind of collective annotated bookmarks collection
The last one is what I personally had in mind initially and I have my own version here:
https://docs.google.com/document/d/1tzS2KU8x31JXoUxmkEr5WikJvxcrgHa4C0vM8LBw49Q/edit?usp=sharing
which anyone is welcome to join in on. It's currently a bit of a mess and not sorted into any real system. I understand from certain replies that some people don't think it's a good idea to make access to other people's work too easy but I think the more fun you have with Pd, without having to learn everything the hard way, the better.
Happy for the links to be nabbed from my wiki and used elsewhere.