Well I ended up answering my own question regarding whether there were other games that used the alternate pseudo hi-res technique employed in Software Farm's Z-Xtricator!
Odyssey Computing released High Resolution Invaders in 1983, a year before Z-Xtricator, and it essentially uses the same technique but achieves it using a more convoluted display driver routine. Unlike Z-Xtricator where everything moves at character level resolution, i.e. 8 pixels, High Resolution Invaders makes efforts to move at finer resolution. This inevitably means that the graphics do not remain perfectly formed as they do in Z-Xtricator, but it does give the game's animation a much smoother feel.
And the software I found on my hard drive: https://trello-attachments.s3.amazonaws ... ements.zip
ZX81, Lambda 8300, Commodore 64, Mac G4 Cube