An update... I made sure no other ini files for mame existed anywhere but the /ini folder of mame. I then focussed on a set of games not known to change between .119 and .120 (i.e. Frogger)
Quite simply put if I put back the .119 version of mame.exe then not only does mamewah let me select the game, but the left/right waggle for OK is honoured and the joystick works within the game.
If I overwrite mame.exe with the .120 version then mamewah still lets me select the game but the left/right OK doesn't work and the joystick doesn't work in the game.
HOWEVER... if I start mame.exe by double-clicking it under Windows Explorer and use its internal menu structure to select the game then the joystick for OK and within the game does work.
I then started fooling around with the mamewah command line. I currently have {nodosbox}{nosafelaunch}. Strangely I find that if I remove either both of them or just one of them then my joysticks start working again with mame .120. With both specified (which worked with .119) then my Ultimarc joysticks don't work.
I don't know why (perhaps Minwah (Mamewah's author) has a theory) but I'm at least somewhat functional again.