FWIW my motivation for working on user32:msg is as follows:

I want to implement MSAA events because I am using them in a program I'm developing separately, that I want to work in Wine. For that, I need to work with the user32:msg tests. So by doing this work, I end up with a cleaner test unit to work with, and I demonstrate that I'm willing to put in the energy to fix the things I'm working on.

Trouble is, that only makes sense if I'm going to be sticking with it long-term. There's an initial learning investment before I can really work on it. I've found that it's rarely useful for me to look at tests in areas where I'm not especially knowledgeable. I simply don't know enough to understand them and work on a credible solution. So from my perspective it's not an incentive problem as I've not even gotten to the point of sending changes in the past.