In my more recent years I've found it easier and lower-friction to get into co-authoring stories with another WAM writer - how this has tended to work is we've set a rough outline and some ground rules then we'll take it in turns to write a page or two before handing over (one of the stories in my list was written exactly this way). Has anyone else had success with this approach? Personally I've enjoyed the surprise of what the other person comes up with while still giving me creativity to springboard off and come up with fun new directions. Or would you say it's more like role-playing than true WAM fiction?

I think your point about agreeing a rough outline and ground rules is very important here.

I tried co-authoring a story a few years back and it later became apparent that whilst I was trying to co-produce something worthy of posting my co-author was more interested in the role-playing aspects of the writing process. This lack of a common understanding ruined it for both of us.

I agree that the writers would need to be on the same page (no pun intended) on the story's tone, the characters, the POV and narration style, and potentially the overall structure if it's a longer story or contains lots of build-up.

At the moment I'm attempting to co-write a series, as I was lucky enough to be contacted by a writer who'd enjoyed my Splatter Dome stories and wanted to collaborate on a sequel. We're still only a few chapters in (my fault), but we spent a long time brainstorming ideas long before starting the actual writing. We used a shared document to map out character profiles, ideas for games and traps, the overall plot, a rough structure, the order of eliminations, plus the arcs for major characters. Even though we're working to a plan, it's still great to see what the other person has come up with.

We typically divide chapters into sections and work in parallel on a shared doc. So far it's been going well, though it'll be a very long time before any of it gets posted. It helped that the co-writer had already written several stories using some of my characters, so I knew that he understood them and that we had compatible styles.

This is quite an interesting suggestion although personally I think I would find it difficult to work with someone else. Probably more because of a selfish motivation to write what I want, although I'm sure the quality and variety of different ideas and approaches would improve the finished article.
Maybe one day.....

I suspect I'm in a similar position. I find my taste in WAM drifting further from the classic custard and pies stuff, and therefore becoming more and more niche. I guess this is another way of saying what everyone already covered: you have to be on the same page (pun intended) from the beginning.

That said, in theory, I love the idea of collaborating. Don't be shy!

Maybe this is a slight tangent, but I got super into graphic novels this year and I would love to work on a WAM one. I can't draw for toffee, so a collab would be the only way to have it be remotely good-lookig. Definitely a tangent now, but related: I highly recommend the Sunstone series.

Years ago I read a tag team co-authored story. That worked well. May have been on the old Splosh Forum. Two authors (male and female) took turns passing the baton. Sounds like you have the same concept - look forward to reading the final story.