Nate, thanks again for your help. Turns out the only (immediately) incompatible lines are app.putCustomOptions and app.getCustomOptions. When I comment out the saveSettings/loadSettings functions, the most recent version of the script (2014-12-04) appears to work fine.
(YESSSSSSSSSSSSS THANK GOD)
When I import the .json created by LayersToPNG into spine, I get a new skeleton created in my project. Is the images directory for the new skeleton supposed to be set automatically? Or is it expected that I have to manually set it to the right location?
Also, I'm attaching the version of the script here for any other people out there also using ancient versions of Photoshop.
I was able to run this version of the script using Photoshop CS2 (v9.0x196)