Ahhh....'tis an interesting Guild, is it not?
There are many possibilities here, and varied are the talents. Personally I got introduced to MW thru Farlandworld and am still actively writing there - the Darmon series is about to take a third step into the unknown. I say unknown, because I really don't know which way it will turn, until now - have a definite plan for the next novel.
The Guild has been a blast. There are so many different possibilities here that there's caramel for Suzy, chocolate covered cherries for Grandma, and the little jaw busters for little Billy. It's a box of chocolates, no doubt.
It started out on the heels of 2009 NanoWrimo, and although most of the work done here (through monthly challenges and prompts) has been of the RP/Fantasy/D&D ilk, there have been some that are strictly non-world building in nature.
I'd like to step in the puddle of the short-response collaborations you suggest, although much of my work has centered around apocalyptic, sci-fi stuff (I like to blow things up). But always ready to twist something and see what comes out.
I have no idea other than the worship of new ideas. Suggest something and we'll run it up the flagpole and see who salutes.
As far as working on your projects, such a thing can be done easily, but I have limited time to offer - as you get older, things aren't necessarily simpler. I'll look into it, though.
Generally I've found that the promts are good exercises and can be taken off in many directions. When people are given a direction that is constricting they tend to have less elbow room and are out of their element. The current 3-part challenge is good as it allows for a lot of differing ideas - our previous challenges centered on themes that were voted upon by everyone (although the voting became arduous) but if you forced yourself to let your imag roam, something would come up. That's why I picked the girl-and-dolly idea in another post in Challenges folder - can go any way you choose. And I thought it might get things moving.