Have you guys ever run a challenge where the idea came from something like spins on a wheel?

Yes!

We’ve done dice roll selections of ponies (single and in pairs)
We’ve had people use a fortune cookie generator to determine their picture theme.
We’ve had people do a few variations of finding something in their environment and drawing based on that.
There’s also the Birthday Games we’ve had people do a few of.

So, not quite a wheel, but same principle of chance :3