I am almost 100% certain that it can indeed spread. I stupidly left several displays very close together including a display with vinegar syndrome. All of the displays apart from the one started out perfect and no signs of vinegar syndrome. After maybe 4-5 months, every single one had vinegar syndrome with most being fairly far along in the deterioration.
Only my experience, but I doubt anyone really wants to test this...
I recently replaced a polarizer on a Duo 280c display, and it isn't too horrible. It requires a lot of patience, a couple of polarizers (in case you mess up) and some care when removing and replacing the polarizer. Also make sure to replace both polarizers if the display has 2 like the 280c.
Replacing the polarizer is cheaper than replacing the display, but you can also break the display in the process, so I would probably try on an old dead display that isnt worth anything first.