Luckily the textures in the .pc.naf files are all at the end of the file.
They are in a format of texture id, texture length, texture, asterix which is easy to split out and rebuild. I just saved the unknown chunk of data before that into a file and then each texture split out into its own file.
I tried a simple test of the main Arkham plack by increasing the texture size from 512 to 1024 and this is what I got.
So at least a full high resolution version of the game would be possible now if anyone has the time and inclination!