No, I got no output after the mouse wheel had stopped working.

But I have a new data point: there seems to be a relation with switching
to the X session of a different user.  I sometimes have several X
sessions running a the same time.  Some minutes ago the wheel had
stopped working.  I switched to the X session at C-M-f2 and then back to
here (i.e. C-M-f1) and the mouse wheel started to work again.

I'm not saying that there is a connection between the failure and other
X sessions, however.  AFAIR, when the mouse wheel stopped working
yesterday there was only one X session running.  Maybe closing the
laptop (suspend to RAM) sometimes triggers this, but that's just
guessing.  That switching X sessions healed the issue didn't seem
incidental, however.  I had the feeling that I should try that, and I
had been using the mouse wheel as first action after switching the X
session back.

But I had been playing stuntrally with the joystick before I noticed the
mouse wheel stopped working.  Maybe plugging in the Joystick is related
again....dunno if that guessing helps you, if not, I'm sorry for the
noise.

Michael.